***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 1 

## Chapter 3: **Te st Pr**  **ocedur es**  Test procedures are a crucial aspect of the heav y- duty vehicle GHG and fuel consumption program. This rulemaking is proposing to establish several new test procedures for both engine and vehicle compliance. This chapter will describe the development proc ess for the test procedures being proposed, including the assessment of engines, aerody namics, rolling resistance, chassis dynamometer testing, powertrain testing, and duty cycles. 

### 3.1 **Heavy -**  **Duty Engine Test Procedure** The agencies are controlling heav y- duty engine fuel consumption and greenhouse gas emissions through the use of engine certification. The program will mirror existing engine regulations for the control of both GHG and non - GHG pollutants in many aspects. The following sections provide an overvi ew of the test procedures. 

### 3.1.1 **Existing Regulation Reference** Heav y- dut y engines currently are certified for GHG and non - GHG pollutants using test procedures developed b y EPA. The Heav y- Dut y Federal Test Procedure (FTP) is a transient test consisting of secon d - by- second sequences of engine speed and torque pairs with values given in normalized percent of maximum form. The cycle was computer generated from a dataset of 88 heav y- duty trucks in urban operation in New York and L os Angeles. These procedures are w ell defined , mirror in - use operating parameters, and thus we believe appropriate also for the assessment of GHG emissions from heav y duty engines . Further, EPA is concerned that we maintain a regulatory

relationship between the non - GHG emissions and GHG e missions, especiall y for control of CO 2 and NO X . Therefore, the agencies are proposing to continue using the same criteria pollutant test procedures for both the CO 2 and fuel consumption standards. For 2007 and later Heav y - Duty engines, 40 CFR Parts 86

– “Control of Emissions from New and In - Use Highway Vehicles and Engines” and 1065

– “Engine Testing Procedures” detail the certification process. 40 CFR 86.007 - 11 defines the standard settings of Oxides of Nitrogen, Non - Methane Hydrocarbons, Carbon Monoxid e, and Particulate Matter. The duty cycles are defined in Part 86. The Federal Test Procedure engine test cycle is defined in 40 CFR part 86 Appendix I . The Supplemental Emissions Test engine cycle is defined in 40 CFR 86.1360(b). All emission measurem ents and calculations are defined in Part 1065, with exceptions as noted in 40 CFR 86.007 - 11. The data requirements are defined in 40 CFR 86.001 - 23 and 40 CFR 1065.695. The measurement method for CO 2 is described in 40 CFR 1065.250. For measurement of CH 4 refer to 40 CFR 1065.260. For measurement of N 2 O refer to 40 CFR 1065.275. We recommend that you use an anal yz er that meets performance specifications shown in Table 1 of 40 CFR 1065.205. Note that your s ys tem must meet the linearity verification of 4 0 CFR 1065.307. To calculate the brake specific mass emissions for CO 2 , CH 4 and N 2 O refer to 40 CFR 1065.650.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

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### 3.1.2 **Engine Dynamometer Test Procedure Proposed**  **Modifications 3.1.2.1**  **Fuel Consumption Calculation** EPA and NHTSA propose to calculate fuel consumption, as defined as gallons per brake horsepower - hour, from the CO 2 measurement, just as in the HD Phase 1 rule. The agencies are proposing that manufacturers use 8,887 grams of CO 2 per gallon of gasoline and 10,180 g CO 2 per gallon of diesel fuel. 

### 3.1.2.2 **Regeneration I mpact on Fuel Consumption and CO**  **2** 

### Emissions The current engine test procedures also require the development of regeneration emission rate and frequency

factors to account for the emission changes during a regeneration event. 1 In Phase 1, the agencies ado pted provisions to exclude CO 2 emissions and fuel consumption due to regeneration. However, for Phase 2, we propose to in clude CO 2 emissions and fuel consumption due to regeneration over the FTP and RMC cycles as determined using the infrequentl y regenerating aftertreatment devices (IRAF) provisions in 40 CFR 1065.680 . However, we are not proposing to include fuel consumption due to regeneration in the creation of the fuel map used in GEM for vehicle compliance Our assessment of the current non - GHG regulatory program indicates that engine manufacturers have significantl y reduced the frequency of regeneration events. In addition, market forces already exist which create incentives to reduce fuel consumption during regeneration. 

### 3.1.2.3 **Fuel Heating Value Correction** In the HD Phase 1 rule, the agencies collected baseline CO 2 performance of diesel engines from testing which used fuels with similar properties. The agencies are proposing to continue using a fuel - specific correction factor for the fuel’s energy content in case this changes in the future. The agencies found the average energy content of the diesel fuel used at EPA’s National Vehicle Fuel and Emissions Laboratory was 21,200 BTU per pound of carbon. This va lue is determined b y dividing the Net Heating Value (BTU per pound) b y the carbon weight fraction of the fuel used in testing. We are also proposing to continue using the Phase 1 corrections for gasoline, natural gas, and liquid petroleum gas in 40 CFR 10 36.530. We are also proposing to expand the table by adding dimethyl ether. In addition to the fuel heating value correction, we are proposing the addition of reference carbon mass fraction values for these fuels to the Table in 40 CFR 1036.530. These reference values are used in the powertrain calculations 40 CFR 1037.550 to acc ount for the difference in carbon mass fraction between the test fuel and the reference fuel prior to correcting for the test fuel’s mass - specific net energy content. The agencies are not proposing fuel corrections for alcohols because the fuel chemistry is homogeneous.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 3 

### 3.1.2.4 **Urea Derived CO 2**  

### Correction The agencies are proposing to allow manufacturers to correct compression ignition engine and powertrain CO 2 emission results (for engines utilizing urea SCR for NO X control) to account for the contribution of ure a derived CO 2 emissions to the total engine CO 2 emissions. Urea derived CO 2 can account for up to 1 percent of the total CO 2 emissions. Urea is produced from gaseous NH 3 and gaseous CO 2 that is captured from the atmosphere, thus CO 2 derived from urea deco mposition in diesel SCR emission control sy stems results in a net emission of zero CO 2 to the environment. In our proposed test procedures for Phase 2, we allow manufacturers to determine CO 2 emissions either by measuring the CO 2 emitted from the engine o r to determine it b y measuring fuel flow rate during the test. If we do not allow for correction of the urea derived CO 2 emissions, this will result in a positive CO 2 bias for CO 2 emissions determined b y measuring the CO 2 emitted from the engine. To perf orm this correction, we are proposing that you determine the mass rate of urea injected over the duty cycle from the engine ’ s J1939 CAN signal. This value is used as an input to an equation that allows you to determine the mass rate of CO 2 from urea durin g the duty cycle. Th is resulting CO 2 mass emission rate value is then used as an input to the steady- state fuel map fuel mass flow rate calculation in 40 CFR 1036 .535 and the total mass of CO 2 emissions over the duty cycle calculations in 40 CFR 1037.550 . Note that this correction is only allowed for CO 2 measured from the engine and not CO 2 derived from fuel flow measurement. The calculation for determination of the mass rate of CO 2 from urea requires the user to input the urea solution urea percent by ma ss . This calculation uses prescribed molecular weights for CO 2 and urea as given in 40 CFR 1065.1005 of 44.0095 and 60.05526 respectivel y . A 1:1 molar ratio of urea reactant to CO 2 product is assumed . To facilitate the ability of the agencies to make thi s correction , we are proposing that the urea mass flow rate be broadcasted on the non - proprietary J1939 PGN (Parameter Group Number) 61475 (and 61478 if applicable) . 

### 3.1.2.5 **Multiple Fuel Maps** Modern heav y- dut y engines may have multiple fuel maps, commonly meant to improve performance or fuel efficiency under certain operating conditions. CO 2 emissions can also be different depending on which map is tested, so it is important to specify a procedure to properly deal with engines with multiple fuel maps. Consistent with criteria - pollutant emissions certification, engine manufacturers should submit CO 2 data from all fuel maps on a given test engine. This includes fuel map information as well as the conditions under which a given fuel map is used ( i.e. transmission g ear, vehicle speed, etc). 

### 3.1.2.6 **Measuring GEM Engine Inputs** To recognize the contribution of the engine in GEM the engine fuel map, full load torque curve and motoring torque curve have to be input into GEM. To insure the robustness of each of those inputs, a s tandard procedure has to be followed. Both the full load and motoring torque curve procedures are already defined in 40CFR part 1065 for engine testing. However, the fuel***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 4 mapping procedure being proposed would be new. The agencies have compared the prop osed procedure against other accepted engine mapping procedures with a number of engines at various labs including EPA’s NVFEL, Southwest Research Institute sponsored b y the agencies, and Environment Canada’s laboratory . 1 The proposed procedure was select ed because it proved to be accurate and repeatable, while limiting the test burden to create the fuel map. This proposed provision is consistent with NAS’s recommendation (3.8). The agencies are proposing that engine manufacturers must certify fuel maps as part of their certification to the engine standards, and that they be required to provide those maps to vehicle manufacturers. The one exception to this requirement would be for cases in which the engine manufacturer certifies based on powertrain testing , as described in Section 3.6 . In such cases, engine manufacturers would not be required to also certify the otherwise applicable fuel maps. We are not proposing that vehicle manufacturers will be allowed to develop their own fuel maps for engines they do not manufacture. 

### 3.1.3 **Engine Fami ly Definition and Test Engine Selection**  **3.1.3.1 Criteria for Engine Families**  The current regulations outline the criteria for grouping engine models into engine families sharing similar emission characteristics. A few of these defining criteria include bore cente r dimensions, cylinder block configuration, valve configuration, and combustion cycle; a comprehensive list can be found in 40 CFR 86.096 - 24(a)(2). While this set of criteria was developed with criteria pollutant emissions in mind, similar effects on CO 2 emissions can be expected. For this reason, this methodology should continue to be followed when considering CO 2 emissions, just as it was in the HD Phase 1 rule. 

### 3.1.3.2 **Emissions Test Engine** We are proposing that manufacturers select at least one engine per eng ine family for emission testing. The methodology for selecting the test engine(s) should be consistent with 40 CFR 86.096 - 24(b)(2) (for heav y - duty Otto cycle engines) and 40 CFR 86.096 - 24(b)(3) (for heav y- duty diesel engines). An inherent characteristic of these methodologies is selecting the engine with the highest fuel feed per stroke (primarily at the speed of maximum rated torque and secondaril y at rated speed) as the test engine, as this is expected to produce the worst - case criteria pollutant emissi ons. To be consistent, however, it is recommended that the same methodology

continue to be used for selecting test engines. 

### 3.2 **Aerodynamic Assessment 3.2.1**  **Aerodynamics for Tractors** For the Phase 1 rule , the agencies promulgated requirements whereb y the coefficie nt of drag assessment was a product of test data and modeling using good engineering judgment. A

1 U.S. Environmental Protection Agency. Memo to Docket EPA - HQ - OAR - 2014 - 0827.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 5 group of aerodynamic bins for tractors corresponding to certain known aerody namic design features ( e.g., Classic, Conventional, SmartWay , etc.) were establish ed based on the results of an agency sponsored aerodynamic assessment test program. The rules require tractor manufacturers to take the aerodynamic test result from a tractor and determine the tractor’s appropriate bin. To ensure the consistency

of the drag assessment results, certain aspects of the truck were defined, including the trailer, location of payload, and tractor - trailer gap. In addition, the agencies specified test procedures for aerody namic assessment: coastdown testing (also used as the ref erence method), wind tunnel testing (reduced and full scale), and computational fluid dy namics (CFD) . Constant speed testing was also permitted as an alternative test procedure, but the agencies did not develop a specific procedure. For the HD Phase 2 pro posal , we are retaining all the current HD Phase 1 aspects of the aerodynamic assessment protocols with the following revisions and additions : enhancement of the anal ys is methodology for the coastdown test procedure , which we are proposing to keep as the reference method for the proposed tractor program ; specifications for the constant speed test procedure; inclusion of trailers in the aerodynamic assessment test protocols; modifications to the reference trailer used for tractor aerodynamic assessment and establishing a reference tractor for trailer aerodyn amic assessment; proposal of wind - average coefficient of drag ( C Dwa) as the required aerodyn amic Greenhouse Gas Emissions Model (GEM) input for tractors ; and considering potential aerody namic performance for advanced aerodynamic performance of tractor - trailer combinations in the proposed timeframe for this rulemaking. Another proposed modification to the aerodynamic assessment for HD Phase 2 is the use of drag area (coefficient of drag multiplied by

the f rontal area , or C

d A ) , rather than the coefficient of drag ( C d), for tractor aerodynamic bin standards. Although this modification would not alter the aerodynamic assessment protocols, it is important to note th is since all HD Phase 2 aerody namic assessment results will be presented in this format , rather than the C d format used for HD Phase 1. 

### 3.2.2 **Modifications to Aerodynamic Assessment Methods**  **for HD**  **Phase 2** Currently , tractor manufacturers are successfull y using the established aerody namic asse ssment methods established unde r HD Phase 1 for implementation and compliance with HD Phase 1 emissions standards. Accordingl y for HD Phase 2, we are proposing to continue to use the existing aerodynamic assessment methods for generating aerodyn amic inputs to GEM with the coastdown test procedure as the reference method , and the constant speed test procedure, wind tunnels, and CFD as the allowed alternative methods (or any other EPA pre - approved test methods). As a result, for HD Phase 2, we are only considering modifications to further enhance, improve or specify the existing aerodynamic assessment methods. During development and since the beginning of HD Phase 1 implementation , we have received suggestions for improving the coastdown t est procedure anal ys is methodology to reduce data post processing and improve data resolution. Also, as mentioned above , although constant speed testing is allowed as an alternative method , we did not define the specifications and protocols for conducting the testing as was done for the coastdown test procedure reference method and other alternative methods. Finally , by virtue of CFD being software - based , it may be possible to improve the conditions specified for performing CFD anal ys is to provide a more realistic result . Accordingl y, for HD Phase 2 aerody namic assessment methods, we are proposing to modify

the coastdown test procedure anal ys is methodology , define the***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 6 specifications and protocols for conducti ng and analyzing the results of the constant speed test procedure, and update the conditions for performing CFD anal ys is. For HD Phase 2, we are not proposing an y changes to the existing wind tunnel specifications and protocols other than revising the meas ured yaw angles to incorporate the wind average coefficient of drag . Under HD Phase 1 , we only required manufacturers to conduct wind tunnel testing at a zero degree yaw angle. In contrast, for HD Phase 2, we are proposing to incorporate the wind average coefficient of drag and, consequentl y, to require measurement at additional yaw angles for generating the yaw sweep curve and calculating the wind average coefficient of drag. W ind tunnels are pivotal in redefining a standard trailer for tractors , assess ing different trailer types to support the proposed trailer standards, and assess ing wind averaged drag. Therefore, the test results using the existing wind tunnel specifications and protocols , and the revisions to incorporate the wind average coefficient of drag will be discussed in the context of these areas later in this section. 

### 3.2.2.1 **Modification of Coastdown Testing**  **Data Analysis Procedures for**  **HD Phase 2**  Based on feedback from the heav y- duty vehicle manufacturing industry and other entities, the a genc ies finalized a Modified SAE J1263 coastdown procedure in the HD Phase 1 rulemaking. During and since the finalization of HD Phase 1 regulations, stakeholders have suggested anal yz ing portions of the data rather than the full data set generated during coastdo wn testing to increase measurement accuracy and/or precision. One OEM suggested the use of the high speed portion of the coastdown test procedure speed range to solel y or predominantly isolate the aerodyn amic forces. Another OEM suggested using the high speed and low speed portions of the coastdown test procedure speed range in an iterative fashion to isolate the mechanical/frictional losses and rolling resistance predominantly present at lower speeds and removing these forces from the higher speed forces to capture predominantly aerodynamic forces. As a result of these suggestions , the agen cies (via contractors IC F Corporation and Southwest Research Institute (SwRI)) coasted down combination tractors on Farm - to - Market H ighway 70 , a rural highway , between Bishop, Texas and Chapman Ranch, Texas. A grade survey was performed by SwRI . Filtered USGS elevation data were also obtained for the same stretch of roadway . 2 The grade information was incorporated into our anal ysis. The testing was conducted overnight, usually between 12 am and 4 am, to minimize traffic and wind. To get a comprehensive data set to conduct various anal ys is techniques, the vehicles were coasted down from 70 mph to 0 mph. Approximately 20 runs (10 in each direction) were planned for each test, but the number was reduced to 14 runs (7 in each direction), due to the increase in test time associated with coasting all the way to 0 mph. An ultrasonic anemometer was mounted 0.85 m above the leading edge of the trailer at the midpoint of the trailer width. This anemometer recorded air speed and direction onboard the vehicle at 10 Hz . A weather station , which measured wind speed, wind direction, temperature, and air pressure at 1 Hz, was placed alongside the road at the approximate midpoint of the stretch of road being used for the tests. Details of the test setup and vehicle information can be found in the on - road testing summary***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 7 report from SwRI. 3 The average and maximum wind speeds were calculated for each run to determine validity

of the run with respect the wind restrictions. Table 3 - 1 below shows the ambient conditions desired during coastdown testing , which resembles the SAE J1263 recommended practice . **Table 3**  **- 1**  **Coastdown Am** **bient Conditions**

PARAMETER RANGE Average wind speed at the test site (for each run in each direction) < 10 mph Maximum wind speed (for each run in each direction) <12.3 mph Average cross wind speed (for each run in each direction at the site) < 5 mph The position of the onboard anemometer is such that the air speed readings need to be corrected. Located above the trailer, the anemometer ’s air velocity readings will ty pically be greater than the free stream air speed. The roadside weather station wa s used to correct the onboard air speed measurements, using the trigonometric calculations below. For this correction, e ach coastdown r un was split into 5 - mph segments , over which the vehicle speed v , measured air speed vr ,meas , wind speed w , and wind direction θ w were averaged.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 8 **Figure 3**  **- 1**  **Diagram of vehicle speed and air speed vectors during coastdowns in opposite directions** 



## v r, th w

θ r, th 

## v r, th w

r, th Direction 1

Direction 2***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 9 The law of cosines was used to calculate the theoretical air speed vr, th from the vehicle speed and weather station measurements , as described in the equation below . The bars over the variables indicate averages over the 5 - mph segments.

r, th = ⎩ ⎨ ⎧ 2 + 2

− 2 cos w , = 1 2 + 2 + 2 cos w , = 2 The resulting theoretical air speed values were regressed against the measured air speed values for every

test, and this linear relationship was used to correct the air speed measurements in the real - time data. This relationship is shown by the equati ons below and from the test results given in Figure 3 - 2 . Regression equation for air speed correction: r, th = 0 + 1 r, meas Applied to air speed measurements: = + ,

**Figure 3**  **- 2**  **Exam ple of theoretical air speed vs. m**  **easured air speed shows a consistent relationship that can be used to correct the onboard air speed measurements.**  vr,th = - 0.872 + 0.937 vr,meas [mph]***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 10 The 10 - Hz data were filtered using a one - second weighted centered moving average prior to further an aly sis. 

### 3.2.2.1.1 High - low Iteration Analysis This analy sis involves analyzing the coastdown over two separate speed ranges. A low speed range is used to estimate mechanical losses and subtract them out of a high - speed range to estimate aerodyn amic drag. This process is iterated until mechanical and aerody namic drag forces converge. The force is not calculated at each measurement, but instead the net force over each speed range is calculated by measuring the time taken to decelerate through each speed range. We assumed a linear decrease in speed (i.e. constant deceleration), because the speed ranges are small. We are also incorporating a simple speed - dependent rear axle loss adjustment to subtract out what we have learned to be a small but speed - dependent non - aerodyn amic drag. We are also in the process of collecting data on the speed effect of tire rolling resistance and are considering including a simple adjustment for this in the final rule. While this analysis can be done for any pair of speed ranges, we are focusing this discussion on a low speed range of 25 to 15 mph and a high speed range of 70 to 60 mph. Table 3 - 2 below describes the analy sis methodology step by st ep.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 11 **Table 3**  **- 2**  **Drag Area Calculation Steps for High**  **- Low Iteration Analysis**  STEP 0: FIND THE TIM ES BRACKETING THE LOW SPEED AND HIGH - SPEED RANGES V LO1 < V I< V LO2 (L OW SPEED) V HI1 < V I< V HI2 (HIGH SPEED) , , , V = VEHICLE SPEED LO1 =15MPH, LO2 =25MPH HI1 =60MPH, HI2 =70MPH Step 1: Calculate acceleration for each speed range. = −

− = ∆ ∆

= −

− = ∆ ∆ a = vehicle acceleration

t = time

Step 2: Calculate average road grade force over each speed range. , = ∆ h ∆ = h − h

−

, = ∆ h

∆ = h − h

− M = vehicle mass

h = elevation (relative) s = travel distance g = gravitational acceleration = 9.81 m/s 2 Step 3: Inertial and Effective Mass (Add 125 lbm per tire to account for rotational inertia). = 125 ∙

= 56 . 7 ∙

= + M inertial = additional inertia from rotating components M e = effective mass n tires = total number of tires in test configuration Step 4: Road load force for each speed range , also accounting for rear axle loss estimate (F

axle ). = − + , − , = − + , − , F = force F axle,lo = 100 N F axle,hi = 200 N Step 5: Air density during each high speed section. = 1000 × P R ( T + 273 . 15 ) ρ = density of air P= average ambient pressure during high speed run in kPa T = average ambient temperature during high speed run in °C R = gas constant for air =287.058 J/(kg-K) Step 6: Average relative air speed over each speed range. , , = ∑ , , = ∑ vr = relative air speed

Step 7: Initial conditions (i=0). Start with no aerodynamic forces in the low speed range. , , = 0***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 12 Step 8: Subtract low - speed aerodynamic forces from low speed forces to estimate mechanical forces. , = − , ,

Step 9: Subtract mechanical forces from high speed forces to estimate aerodynamic forces. , , = − , Step 10: Adjust aerodynamic forces by speed to estimate low - speed aerodynamic forces. , , = , , , ,

, , Step 11: Repeat steps 8 - 10 until both high - speed aerodynamic and low - speed mechanical forces both converge less than 1%. Repeat steps 8 - 10 until: 1 − , ,

, , < 0 . 01 and 1 − , ,

, , < 0 . 01 Step 12: Calculate drag area. = 2 , ,

, , There are some advantages to using this method over the Phase 1 method. F ocusing on segmented speed ranges may open up more test locations, as less road or track space would be required to collect a full data set. The middle range of speeds that would be eliminated contains a higher proportion of rolling resistance forces and also sweeps through greater yaw angles, even at mod est crosswind conditions, which can increase the aerodynamic drag of certain runs and subsequently

in crease the variability

of a test. This method does not account for yaw angle, but with the proper wind constraints and the use of a high - speed range to estimate aerody namic drag, the yaw angle effect should be small or statistically indiscernible. The re sult of this analy sis method is considered to be a zero - yaw C d A . 

### 3.2.2.1.2 High - low Intercept Analysis This method is similar to the previous method, with a few important differences. Instead of calculating force over speed intervals, like in the iteration method, the force is calculate d at every speed measurement, similar to the HD Phase 1. T he mechanical forces are determined through the low speed range that goes all the way to 0 mph though a force versus vehicle speed regression . The force intercept is then adj usted by a generic rolling resistance speed adjustment to estimate rolling resistance forces throughout the coastdown. These forces are then subtracted***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 13 from the total road load forces to estimate aerodyn amic drag forces. The aerody namic drag forces are then adjusted for yaw angle through an adjustment previous determined by a CFD run. The agencies did not evaluate this method in detail for the proposal due to lack of CFD or other yaw sweep data for the specific tractors that were tested. The agencies al so did not have data to support a specific rolling resistance speed correction. The agencies are in the process of collecting some of this data and may evaluate this method for the final rule. 

### 3.2.2.1.3 High -speed Yaw Angle Analysis Another suggested anal ysis metho d was to use only the high - speed range from each coastdown (70 - 50 mph) and use the onboard anemometry to develop a wind - average C d A , as opposed to a zero - yaw C d A . One main advantage to this method is that it would allow for less road or track space to be used because onl y a high speed range would be needed. This allows for minimal acceleration and deceleration, which consume significant amounts of space and time, and subsequentl y allow s for more runs to be conducted. A second - order regression with no linear term is used to separate the mechanical forces from the aerodynamic forces; the regression is done similar to Phase 1, but using the smaller speed range and air speed instead of vehicle speed.

= ∆ ∆ = + The D coefficient is used to estimate drag area C d A , using the temperature and pressure during the speed range to calculate air density , just as in the anal ys is methods discussed earlier in this section . The yaw angle θ r is averaged over the speed range , and the absolute value is used. The C d A is fit to a second order regression with the absolute value of the yaw angle.

= 2

d = 0 + 1 r + 2 r 2 This C

d A curve would then be used to conduct a yaw sweep to develop a wind - average C d A value for certification, rather than a zero - yaw C d A . While air direction was measured onboard, the accuracy

of the anemometer is onl y ± 2° , according the product specifications . 4 Over the speed range recommend for anal ys is, yaw angles would onl y occur be tween 0° (for a direct headwind/tail wind) and 6° (for a direct crosswind). The accuracy of the instrument is not sufficient to measure average yaw angle. Instead, the roadside weather station was used to more accuratel y determine the average yaw angle. Trigonometric equations using the weather station measurements were used to calculate the average yaw angle for each coastdown run; the anemometer air direction readings were not used . The yaw angle was ca lculated using the law of sines. See Figure 3 - 1 earlier for variable references.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 14 r = r , th = ⎩

⎨ ⎧ sin − 1 sin w , = 1

− sin − 1 r sin w , = 2 Using the recommended speed range (70 - 50 mph) and regression fit equation, we found that the standard errors for the D values for individual runs ranged from 1 6 to 76 percent , with a median value of 31 percent . The standard error for the A value w as even larger, ranging from 25 to 186 percent . These values are extremely high, compared to appl yi ng this method through the full speed range (70 - 0 mph), where the median of the standard errors for the D values was approximately

3 to 4 percent . In a ty pical unlo aded coastdown from 70 to 50 mph, the average vehicle speed is approximately

59 mph. The SAE J1263 and HD Phase 1 limit for cross wind is 5 mph. Under this limiting scenario , the average yaw angle experienced during this speed range would be 4.8° [ tan - 1 ( 5/59)]. This does not provide a large enough spread in yaw angle to develop a yaw sweep to produce a statisticall y meaningful wind averaged drag area. Furthermore, if winds are relativel y constant throughout a test, the constant cross wind would provide yaw angles around 5° and - 5°, without much in between. If winds are not exactly perpendicular, then there would be more of a distribution closer to 0°, but with less data at wider angles. The data collected here show that the bulk of the yaw angles from the data collected within Phase 1 wind requirements falls between - 4° and 4°. Further analy sis shows that statistically

significant curves of C d A versus yaw angle could not be formed due to the variability of the data. Since the absolute value of the yaw angle is used in the anal ys is, this method also assumes that the aerodyn amic characteristics are sy mmetrical , which is a not a safe assumption. Even usin g the absolute values, the C d A versus yaw angle curve is not statistically meaningful, as shown in Figure 3 - 3 .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 15 **Figure 3**  **- 3**  **Exam ple data from** **the high -**  **speed yaw angle analysis shows high uncertainty of the statistical fit. The solid line is the yaw curve with the dashed lines representing the upper and lower 95% confidence limits**  **of the m ean.** ***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 16 A fter evaluating the methods described above, the agencies are proposing that the high low iteration anal ys is method be used to determine the drag area GEM input. Ingeneral, while coastdown tests are used to determine the aerodyn amic drag, the procedure itself is a road load procedure, not an aerodynamic one. That is, the measured or calculated forces represent the total road load from which the aerodynamic forces must be calculated or inferred; they are not measured directl y. As a result, all anal ys is methods that are used in conjunction with coastdowns must calculate or infer aerodynamic forces. 

### 3.2.2.2 **Specifications and Protocols for Conducting Constant Speed Testing**  Similar to the Coastdown Test Procedure, the Constant Speed Test Procedure is conducted on road and used to measure the forces acting on the tractor. In contrast to the Coastdown Test where the vehicle is accelerated to a set speed and then allowed to coast to a lower speed in neutral , the Constant Speed Test is conducted by measuring torque al ong the driveline at various constant speeds. This helps to reduce measurement uncertainty due to potential driveline vibration experienced during coastdown and better isolate the force contributions between speed transitions over the speed range (e.g., a erody namic drag dominance at high speed; a mix of aero drag and mechanical/frictional forces in middle speeds; and mechanical/frictional force dominance at low speeds). In addition, whereas the total force, and consequentl y the total drag force, is derive d based on the speed and time for the coastdown test, the constant speed test measures the total force at the wheels using wheel hub torque meters and/or a driveshaft torque meter . It can also incorporate, where needed and available, engine speed and torq

ue, transmission gear ratio, rear axle losses , or other relevant data . The constant speed test has the potential to reduce uncertainty compared to a coastdown because it can collect data at a single speed for a sustained amount of time. For HD Phase 1, w e allowed the use of Constant Speed testing as an alternate aerodynam ic method but did not promulgate specific test procedure requirements. In lieu of this, a manufacturer would have been required to develop its own test procedure for constant speed testi ng and submit it to the agencies for approval. For HD Phase 2, we are proposing specific requirements for conducting the constant speed test , to be used by manufacturers choosing this testing method . Accordingl y, we evaluated the constant speed testing us ing the same vehicles receiving the coastdown test procedure. For our evaluations, we used several speeds to determine the optimal speeds for constant speed testing. In addition, we performed the testing with both wheel hub torque meters and a driveshaft torque meter to quantify the benefits and detriments of both methods. More details on our test set up for constant speed testing and our results are discussed below. In addition to evaluating the constant speed test procedure, we are also seeking comment regarding making the constant speed test procedure the reference aerodynamic method . We received suggestions to this e ffect from industry during the HD Phase 1 rulemaking process, since some of the OEMs have European controlling interest. Thus, use of the constant speed test would allow them to harmonize test procedures with their European counterparts , who are required to use constant speed testing . W e did not have data to support use of the constant speed test as the preferred method for Phase 1 . Since then we have evaluated and are proposing specific constant speed testing requirements for HD Phase 2. Thus, we are taking this opportunity

to explore this approach again.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 17 

### 3.2.2.2.1 Constant Speed Test Procedure Specifications For our evaluation of the constant speed test, we used the following procedure and specifications:  Use d four High Resolution Truck Torque Wheel Transducers with approximate 5 lb - ft resolut ion during testing of each of the tractor s. Mechanical protection against high torque application (both acceleration and braking) telemetry , and associated wheel adapters, encoder, amplifier, and power suppl y was employed.  Used an in - line strain - gauged to rque flange, which was used to measure driveshaft torque during the testing each of the tractor s (i.e., driveshaft torque sensor). The torque flange was an ANSI C12.20 0.5 class meter with a range of 0 to 5,000 Newton - meters (N - m). This torque meter uti lizes special adapters and cannot be connected directly to the drive shaft. A modified drive shaft shall was acquired for each tractor to accommodate the torque meter. These drive shafts were dynamically balanced.  Used a driveshaft torque sensor and whee l hub meter simultaneously to collect data at the drive shaft and the wheels for comparison. The driveshaft torque sensor was calibrated according to 40 CFR 1065.310.  During the test, the following parameters were monitored (data collected) , similar to th e coastdown tests : o Air speed data using an anemometer mounted on the trailer approximately 0.85 m above the trailer roof, at the midpoint of the trailer width, at the leading edge of the trailer. o Vehicle speed using an optical fifth wheel. o Engine speed using the electronic control unit (ECU). o Grade data along the location of track or road where testing was performed .  The vehicle was warmed - up by being driven for 30 minutes prior to the test. The same road was used for the constant speed testing coastdown to ensure grade/location consistency .  Testing was performed at the following speeds and d urations while recording torque and engine data. Cruise control was used to maintain speeds, except f or the lower one or two speeds for certain tests . o 10 mph

– 7.5 minutes in each direction o 20 mph

– 7.5 minutes in each direction o 30 mph

– 7.5 minutes in each direction o 50 mph

– 8 - 10 minutes in each direction o 70 mph

– Approx imately 11.25 mi les or 9.6 minutes in each direction.  If necessary , multiple passes were conducted. The agencies conducted constant speed testing through Southwest Research Institute along the same stretch of roadway as the coastdown testing. 

### 3.2.2.2.2 Constant Speed Test Procedure Analysis Methodology For analy sis of the constant speed test procedure data, the 10 - Hz data were filtered using a two - second centered moving average and then split into 10 - second segments over which the***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 18 forces, air speed, and air direction were averaged. For tractors equipped with the driveshaft torque meter, the road load force was calculated as follows:

, = ∙ + For tractors also equipped with the wheel torque meters, the road load force was calculated as follows:

, = + Where : τshaft = driveshaft torque ω eng = engine speed GR = transmission gear ratio F RL ,shaft = road load force calculated from the driveshaft torque τ wheel = wheel torque , sum of all four wheel torque measurements ω wheel = wheel speed , average of all four wheel speed measurements F RL ,w heel = road load force calculated from the wheel torque The anal ys is method involved a force subtraction method where the average road load force at 10 mph was assumed to be made up of just rolling resistan ce and mechanical forces. This value was subtracted from each 50 - mph and 70 - mph road load force measurement to estimate aerodyn amic forces , and C d A was calculated similar to coastdowns .

= , = − ( 50 & 70 mph runs onl y)

= 2 Since wind conditions would vary from one test day

to another, the yaw angle would also change, creating larger yaw angles and different yaw angle spreads for some tests. In order to compare the constant speed results to one another , the C d A values were regressed against a fourth - order pol ynomial of yaw angle to determine the zero - yaw C d A . Any tests that were conducted outside of the wind speed constraints were included along with tests within the wind constraints because the yaw angle distribution helped developed the poly nomial fit. ( ) = ( 0 ) + + + + If over 75 percent of the points occurred at yaw angles between - 2 and +2 degrees, then the zero - yaw C

d A was determine d by using the average of the C d A v alues between those yaw angles. This would occur on test day s where the prevailing winds were more parallel to the direction of travel, resulting in low yaw angles. A regression was not used in this case because the F test showed a low level significance of the poly nomial fit given above . These regressed or***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 19 averaged zero - yaw C d A values are the constant speed test results that are reported in this document. Since the wheel torque measurements are downstream of the rear axle losses, they are a more accurate measurement of actual road load forces than the driveshaft torque measurements . The first several tests were conducted without wheel torque meters, so those tests’ results, which were determined onl y through the driveshaft torque measurements, were reduced b y 6 percent , based on the ratio of C d A determined from one of the vehicles with a similar axle that was equipped with both driveshaft and wheel torque meters. 

### 3.2.2.3 **Results for Coastdown and Constant Speed Testing**  **Using Modified/Specified**  **Test Proced**  **ures** Using the coastdown test procedure with modified anal ys is methodology and the specifications and protocols for the constant speed test procedure, we evaluated four Class 8, high roof sleeper cabs, one from each of the heavy- duty tractor OEMs, and a Cl ass 8, high roof, tandem axle sleeper cab with a 53’ dry box van trailer. The results using these procedures on tractor - trailer combinations with the trailer in the standard configuration (e.g., a 53’ dry box van with no trailer devices installed) are sho wn below in Table 3 - 3 and Table 3 - 4 for the coastdown and constant speed test procedure, respectivel y. **Table 3**  **- 3**  **Summary of Results from Coastdown Testing**  CAB T YPE ROOF

H EI GHT TRAILER

CONFIGURATION C d A [ m2 ] ST D.

E RROR # OF VALID

R UNS Sleeper 1 High Standard 5.9 0.5 % 14 Sleeper 2 High Standard 6.2 2.1 % 14 Sleeper 3 High Standard 6.1 2.3 % 14 Based on this test procedure, the results from our constant speed testing are shown in Table 3 - 4 below. **Table 3**  **- 4**  **Summary of Results from Constant Speed Testing** 

CAB TYPE ROOF

HEIGHT TRAILER

CONFIGURATION C d A [ m2 ] STD.

ERROR Sleeper 1 High Standard 6.1 0.7 % Sleeper 2 High Standard 5.9 1.8 % Sleeper 3 High Standard 5. 9 0. 3 % The coastdown and constant speed results show a similar range of C d A values. Using different speed ranges in the coastdown method or anal ys is techniques in either method may produce slightly

different C

d A range s , depending on certain factors such as the temperature and speed dependence of tire rolling resistance . T he uncertainties , however, are unlikel y to change significantl y, since they are based on run - to - run variability

for a given anal ys is technique. To ensure the required test repeatability***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 20 and method acceptance needed for future certification and compliance purposes, we looked at the standard error of the test and the alignment between the test procedures for each tractor. The standard error of the constant speed tests was determined through the statistical fit of the ten second segments through the yaw pol ynomial where the pol ynomial fit was used . In this case, the standard error represents that of the zero - yaw C d A from that fit . Otherwise, the standard error is of the mean of the C d A values between - 2 and 2 degrees. This may slightly underestimate the uncertai nty due to the precision error that may be introduced in the low - speed segments. Other trailer configurations tested with coastdowns show lower uncertainties than the standard trailer. C onsequently , either on - road test should be acceptable for aerodyn ami c assessment . The agencies are still collect ing data using both test procedures and will continue to evaluate the accuracy and repeatability

of both. Accordingl y , we are proposing to require the use of the coastdown test procedure as the reference method with the high - low iteration analy sis method discussed above . We are also specif yi ng the constant speed aerody namic assessment test procedure based on our above anal ys is . F or constant speed testing, m anufacturers may use a driveshaft torque meter or wheel hub torque meters for constant speed testing provided they meet or exceed the specifications given above for each typ e of device. We are completing testing on an additional sleeper cab tractor from another OEM and on a day cab tractor. Although all of th e on - road testing for tractors is not complete, we believe the results of future on - road testing will be consistent with the trends emerging from the existing data . Once all on - road testing is complete, a full report will be included in the docket and further considered in the context of the tractor aerody namic standards . 

### 3.2.2.4 **Modifications to Computational Fluid Dynamics**  **for HD**  **Phase 2** Computational Fluid Dynamics, or CFD, capitalizes on today ’s computing power by modeling a full size vehicle and simulating th e flows around this model to examine the fluid dy namic properties, in a virtual environment. CFD tools are used to solve either the Navier Stokes equations that relate the ph ys ical law of conservation of momentum to the flow relationship around a body in motion or a static body with fluid in motion around it, or the Boltzmann equation that examines fluid mechanics and determines the characteristics of discreet, individual particles within a fluid and relates this behavior to the overall dy namics and behavi or of the fluid. CFD analy sis involves several steps: defining the model structure or geometry based on provided specifications to define the basic model shape; appl yi ng a closed surface around the structure to define the external model shape (wrapping o r surface meshing); dividing the control volume, including the model and the surrounding environment, up into smaller, discreet shapes (gridding); defining the flow conditions in and out of the control volume and the flow relationships within the grid (inc luding eddies and turbulence); and solving the flow equations based on the prescribed flow conditions and relationships. This approach can be beneficial to manufacturers since they can rapidl y prototy

pe ( e.g. , design, research, and model) an entire vehicle without investing in material costs; they can modify and investigate changes easil y; and the data files can be re - used and shared within the compan y or with corporate partners.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 21 For HD Phase 1, w e established some CFD procedures based on our results and industry collaboration since there were no standardized practices at the time. In addition, to ensure data consistency , a minimum set of characteristics and criteria was included for CFD anal ys is to ensure that the boundary

and surface conditions are not too coarse and, thus, not representative of the real tractor and environmental conditions. For HD Phase 2, we are proposing to either use the existing criteria from HD Phase 1 or require adherence to a newly established, Society

of Automotive Engineering (SAE) standard for CFD, SAE J2966. 5 Accordingl y, we are comparing the criteria we set forth in HD Phase 1 with SAE J2966 to assess the efficacy of adopting this new standard. In addition, we are considering enhancements to the specified conditions for pe rforming CFD anal ys is. Specifically , we specified the use of a simulated vehicle speed of 55 miles per hour and “ambient conditions consistent with the coastdown test procedures.” These conditions are ambiguous and may

require greater specificity to ensure that the CFD analy sis is more closely simulating the real world conditions. As a result, we are seeking comment on the need to improve the simulated ambient environmental conditions for conducting CFD anal ys is. Also, similar to wind tunnels, we are pro posing to modify the measured yaw angles used in the CFD anal ys is to incorporate the concept of the wind average coefficient of drag. Under HD Phase 1, we onl y required manufacturers to perform the CFD analysis at a zero degree yaw angle. For HD Phase 2, we are requiring the CFD anal ys is to be performed at additional yaw angles for generating the yaw sweep curve and calculating the wind average coefficient of drag. This is discussed further in the following section. Finally , our CFD specificatio ns do not include or require the use of turbulence intensity in the CFD anal ys is, and the use of a turbulence model is only required “if applicable.” As a result, there is less ability to capture transient flow phenomena in the CFD anal ys is. Based on dev elopments since HD Phase 1, the ability to include turbulence in the CFD anal ys is without severel y impacting the analy sis run time has improved. Therefore, we are seeking comment on the inclusion of turbulence in CFD anal ys is. A s we consider these propos ed modifications and a revised standard reference trailer for tractor aerodynamic assessment, it is important to evaluate the ability of CFD to characterize the aerodynamics when aerodynamic trailer devices are emplo yed. Therefore, we will be evaluating trailer aerodynamic devices for CFD method validation to support HD Phase 2. 

### 3.2.3 **Aerodynamic Assessment and Use of Wind Average d**  **Drag Area** Finally , we received comments in HD Phase 1 regarding the use of the wind averaged coefficient of drag ( WAC d) since WAC

d accounts for aerodyn amic performance across a broader spectrum of wind conditions rather than a pure headwind or tailwind (e.g., zero degree yaw). Consequently , the use of WAC d for aerodyn amic assessment may better reflect real - world aerodynamic performance and fuel consumption . Therefore, we assessed the use of WAC d for HD Phase 2 and the results are discussed below in this section.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 22 EPA and NHTSA recognize that wind conditions have a greater impact on real world CO 2 emissions and fuel consumption of heavy- duty tractor s than light - duty vehicles. As stated in the NAS report 6 , the wind averaged drag coefficient is about 15 percent higher than the zero degree coefficient of drag ( C d). The large ratio of the side area of a combination tractor and trailer to the frontal area illustrates that winds will have a significant impact on drag. One disadvantage of the agencies’ approach to aerodynamic assessment in Phase 1 is that the test m ethods have varying but limited degrees of ability to assess wind conditions. Wind tunnels are currentl y the onl y demonstrated tool to measure the influence of wind speed and direction on a vehicle ’s aerodynamic performance. The coastdown test and comput ational fluid dy namics modeling both have limited ability to assess yaw conditions. The constant speed test has the potential for yaw angle measurement capability but it is not certain how its ability to measure the influence of wind speed and direction o n a vehicle’s aerodynamic performance compares to the wind tunnel. To address this issue in HD Phase 1 , the agencies finalized the use of coefficient of drag values that represented zero yaw (i.e., representing wind from directl y in front of the vehicle, not from the side). The agencies recognized that the results of using the zero - yaw approach will produce fuel consumption results in the regulatory program which are slightly lower (i.e. predict better fuel consumption results) than in - use , but we believe d this approach was appropriate since not all manufacturers were using wind tunnels for the aerodyn amic assessment to the extent needed for wind averaged C d quantification purposes. During HD Phase 1, we examined full yaw sweep data from the reduced - scal e wind tunnel test for three manufacturer 1/8 th scale models. Below in Figure 3 - 4 are the yaw sweep graphs for three manufacturer s’ vehicles in the reduced - scale wind tunnel with the WA C d shown for comparison. This graph indicates that, although the zero - yaw C d results for two tractors can be nearl y identical at zero yaw, their aerodynamic performance may diverge as the yaw angle is increased. As a result, although the two tractors exhibit similar zero - yaw aerodynamic performance, their aerody namic performance in non - zero yaw conditions may be drastically different and, consequently , so would their real - world fuel efficiency .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 23 **Fig ure**  **3 -**  **4 Full yaw sweeps and wind**  **- average coefficients of drag (**  **WAC d**  **s) for three manufacturer, 1/8th scale, tractor m**  **odels in the reduced scale wind tunnel.** 0. 000 0. 050 0. 100 0. 150 0. 200 0. 250 0. 300

- 10.000 - 8.000 - 6. 000 - 4. 000 - 2.000 0. 000 2.000 4.000 6. 000 8. 000 10.000 Tr uck A Yaw Swe ep Tr uck A WACd Tr uck B Yaw Swe ep Tr uck B W ACd Tr uck C Yaw Swe ep Tr uck C W ACd***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 24 Table 3 - 5 below shows the results of an anal ys is on the impact of improving the non - zero yaw performance on the coefficient of drag for Tractor A versus Tractor B and Tractor C, respectivel y . **Table 3**  **- 5**  **Absolute Deltas and Percent Difference for Individual Yaw Points for Tractor A versus Tractor B and Tractor C**  **.** +/ - YAW ANGLE AVERAGES TRACTOR A VERSUS TRACTOR B TRACTOR A VERSUS TRACTOR C Delta C

d Delta C d % Difference Delta C d Delta C d % Difference Zero Degree 0.001 0.18% - 0.031 - 5.84% One Degree - 0.003 - 0.53% - 0.035 - 6.65% Three Degrees - 0.018 - 3.33% - 0.052 - 9.58% Six Degrees - 0.035 - 5.85% - 0.078 - 13.05% Nine Degrees - 0.042 - 6.24% - 0.098 - 14.52% Based on the results, although Tractor A and Tractor B have similar zero degree aerodynamic performance, their aerodynamic performance at high er yaw angles results in a 0.53 to 6.24 percent loss in aerody namic efficiency . This difference is exacerbated fo r the case of Tractor A versus Tractor C where the zero degree performance of Tractor C is worse than Tractor A. Due to this decreased aerody namic performance at each individual yaw angle, the WAC d values are impacted as follows when again comparing Tracto r A versus Tractor B and Tractor C, respectivel y, as shown in Table 3 - 6 . **Table 3**  **- 6**  **Absolute Deltas and Percent Differen ce for**  **Wind Averaged**  **Coefficient of Drag ( WAC**  **d ) for**  **Tractor A versus Tractor B and Tractor C.** COMPARI SON ABSOLUTE

DEL TA %

DI FFERENCE Tractor A vs . B - 0.021 - 3.5% Tractor A vs . C - 0.069 - 11.7% Consequently , by

focusing solel y on zero degree yaw angle drag, there is an additional 3.5 to 11.7 percent of benefit lost due to higher aerody namic drag at greater yaw angles. As a result of this data and comments we received during and since HD Phase 1 , we are proposing the use of additional yaw data to develop a wind - average drag area to be used for input into the GEM model and assigning a GHG emissions score. Further, the agencies are proposing to require manufacturers to use the yaw sweep calculation in SAE J1252 to determine WAC d and, coupled with the frontal area, the wind averaged drag area ( WA C d A ) . Specificall y, we are proposing to require the C d A data for zero degrees, positive/negative one degree, positive/negative three degrees, positive/negative six degrees and positive/negative nine degrees to calculate WAC d A . This is in accordance with SAE J1252 which requires a minimum of six points for the calculating WAC d rather than just using zero degrees as is***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 25 currentl y required for the HD Phase 1 version of GEM input and positive/negative six degrees currentl y used for the generation of the HD Phase 1 WA C d as a yaw sweep correction factor. This proposed methodology would appl y for an y aerodynamic method that is used to generate the WAC

d using an approved series of yaw angles. Alternativel y, a manufacturer may use request to use a series of different angles (e.g., 0, ±2, ±4, ±6, ±8 , ±10 degrees) or fewer angles (e.g., ±3, ±6, ±9) with advanced approval b y and demonstration to the agencies that the series of different/reduced yaw angles provides equivalent results to the required yaw angles. We will also need to generate a yaw sweep curve and WA C d A based on the coastdown reference method results to determine the appropriate GEM model inputs . At present, the coastdown p rocedure does not account for the varying wind direction well enough to reliably generate a yaw sweep curve. Therefore, one approach we are proposing to require is for a manufacturer to generate the yaw sweep curve using an alternate method , in particular, the wind tunnel or CFD , by taking the differential of the coastdown result and zero - yaw result from the alternate method and additively appl yi ng the coastdown - alternate method zero yaw to each of the points on the alternate method yaw sweep cur ve. Both of th ese technique s are demonstrated below in Figure 3 - 5 .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 26 **Figure 3**  **- 5**  **Proposed development of a c oastd**  **own yaw sweep curve based on additive offset from alternate**  **method yaw sweep curve.**

0.531 0.724 0.801

0.607

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

-10.000 -8.000 -6.000 -4.000 -2.000 0.000 2.000 4.000 6.000 8.000 10.000



## Ya **w Sweep Curve Shift Concept** Multiplicative Approach

Additive Approach***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 27 Using the results in Figure 3 - 5 as it applies to the entire yaw sweep curve ; a multiplicative approach changes the shape of the yaw sweep curve whereas the additive approach maintains the yaw sweep curve shape. Therefore, the additive approach is a more appropriate to use than the multiplicative approach when using the full yaw sweep curve to generate the coastdown yaw sweep curve. This, however, requires the addition of the offset to each point on the yaw sweep curve, to shift and maintain the shape of the yaw sweep curve, and recalculating the wind average drag area based on the shifted curve. Alternativel y, a simpler approach is to use the offset s between the zero degree yaw and the coastdown values to calculate F alt - aero ; the zero degree yaw and WAC d A values to calculate a wind average drag offset from the alternate method ; and apply them to the coastdown result s which reduces the complexity of calculating a virtual coastdown wind average drag area . This approach is explored in further detail in Section 3.2.9 . Accordingl y, we are proposing to require WAC d A as the aerodynamic GEM input for HD Phase 2 and invite comm ent on the methodology used to generate a coastdown equivalent WAC d A . Although the data above is shown in C d form at , we will use WAC d A format for alternate method results for HD Phase 2. The WAC d A values used to support HD Phase 2 are discussed below in Section 3.2.9 . 

### 3.2.4 **HD Phase 1 Yaw Sweep Correction** In this propos al , the agencies propose to correct the Phase 1 yaw sweep correction factor equation to create equival ency between the two methods currentl y allowed by the regulations to determine the yaw sweep coefficient of drag area . The HD Phase 1 aerodynamic bins are based on zero degrees yaw. However, the current regulations allow manufacturers the option of deter mining the aerody

namic bin levels based on their wind average drag performance relative to the nominal wind averaged drag performance of the baseline fleet evaluated in Phase 1. The yaw sweep correction factor, as defined currently in 40 CFR 1037.521, all ows the determination of the C D A based on (1) averaging the measurements at positive six degrees and negative six degrees (± 6 degrees) of yaw and (2) a full yaw sweep as defined b y SAE J1252. However, these two methods do not produce the same wind averag ed drag C D A value , as shown below in Table 3 - 7 . The C D A based full yaw sweeps produce lower values, on the average of 3.3 percent.

**Table 3**  **- 7**  **: C** 

**D A**  **Values** C D A (ZERO YAW) C D A (AVG ± 6 DEGREES) C D A (FULL YAW SWEEP) Sleeper Cab 1 5.425 6.23 9 6.043 Sleeper Cab 2 5.553 6.61 9 6.405 Sleeper Cab 3 5.622 6.442 6.285 Sleeper Cab 4 5.563 6.66 3 6.373 The value used to represent the nominal wind average drag performance of the fleet developed for Phase 1 was based on ± 6 degree measurement values. In order to remove the discrepancy

in measurement methods, the agencies developed a new factor for determining the yaw sweep correction factor for data based on full yaw sweeps. We propose that manufacturers use the following equation when using wind averaged drag values based on the full yaw sweep.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 28 CF ys = [ C

D A from full yaw sweep * 0.8330] / [ C D A at zero yaw] 

### 3.2.5 **Aerodynamics for Trailers** For HD Phase 2, the agencies are proposing GHG standards reflecting GHG and fuel consumption reductions from trailers. Aerody namic improvements are among the technologies on which those proposed standards are predicated. New aerodynamic technologies have been implemented on box trailers to improve their aerody namic efficiency

and lower overall tractor trailer fuel consumption. Inaddition, the agencies have assessed the extent that some of these technologies may migrate to the trailer sector without regulation, and the extent these improvements should be reflected in the reference trailer used in tractor certification testing. Consistent with the proposed trailer regulations, our aerodyn amic assessment of differ ent trailer configurations (applicable to coastdown, constant speed and reduced - scale wind tunnel testing) and trailer types (applicable to reduced scale wind tunnel testing only) was limited to box van ty

pe trailers including dry

box, reefer, and pup. Sp ecifics on the applicable trailer types and certification protocols are discussed further in Section IV . D(2), of the preamble. 

### 3.2.5.1 **On -**  **Road Aerodynamic Assessment of Different Trailer Configurations**  W e are also proposing to use the on - road test procedures as o ne method to determi ne aerodynamic performance for the proposed trailer program . Specifically , the on - road testing would estimate the delta drag area between a tractor - trailer combination for a trailer equipped without and with aerodynamic trailer devices (i.e., A to B testing; A constitutes a test without the technology ; B constitutes a test with the technology) . In addition , we used these test procedures to evaluate the ability of on - road testing to capture the aerodynamics of trailers equipped with and without aerodynamic devices for the standard trailer used in the tractor program . Consequently , we assess ed different trailer configurations using the proposed coastdown and constant speed test procedures with and without trailer aerody namic devices ins talled on the trailer . Specifically , we performed coordinated, HD Phase 2 and SmartWay testing on - road for 53’ dry box van trailers; which represent the bulk of the trailer market. The results of testing 53’ dry box van trailers in different configuratio ns are shown below in Table 3 - 8 and Table 3 - 9 . **Table 3**  **- 8**  **Summary of Results from Coas**  **tdown Testing with Different Trailer Configurations**  CAB TYPE ROOF

HEIGHT CONFIGURATION C **d** A [ m2 ] STANDARD

ERROR DELTA C **d** A

(VS. STANDARD) % DELTA C **d** A

(VS. STANDARD) Sleeper 1 High Standard 5. 9 0.5% -- --

With Trailer Skirt 5.4 1.0% 0.5 8.5% With Trailer Skirt and Boat Tail 5.0 1.0% 0.9 15 % Sleeper 2 High Standard 6. 2 2.1% -- --

With Trailer Skirt 5.6 1.3% 0.6 10 % With Trailer Skirt and Boat Tail 5.1 1.1% 1.1 18 % Sleeper 3 High Standard 6.1 2.3% -- --

With Trailer Skirt 5.6 1.2% 0.5 8.2% With Trailer Skirt and Boat Tail 5.4 1.1% 0.7 11%***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 29 **Table 3**  **- 9**  **Summary of Results from Constant Speed Testing**  CAB TYPE ROOF

HEIGHT CONFIGURATION C **D** A [ m2 ] STANDARD

ERROR DELTA C **d** A (VS. STANDARD) % DELTA C **d** A (VS. STANDARD) Sleeper 1 High Standard 6.1 0.7% -- -- With Trailer Skirt 5.2 2.2% 0.7 12% With Trailer Skirt and Boat Tail 4.9 0.7% 1.2 20% Sleeper 2 High Standard 5.9 1.8% -- -- With Trailer Skirt 5. 5 0.7% 0. 4 6.7 % With Trailer Skirt and Boat Tail 5.1 1.0% 0. 8 14 % Sleeper 3 High Standard 5.9 0.3% -- -- With Trailer Skirt 5.7 0.4% 0.2 3.4% With Trailer Skirt and Boat Tail 5.2 0.6% 0.7 12% In addition to our on - road testing of 53’ dry box vans , we are coordinating with the California Air Resources Board (ARB) and U.S. Department of Energy ’s (U.S. DOE) National Renewable Energy

L aboratory

(NREL) to evaluate twin, 28 - foot (also known as “pup”) trailers using the coastdown and the SAE J1526 Ty pe III 7 test procedure. Also, we are planning additional on - road testing of reefer box van trailers in the same location and identical tractors used for our evaluations of 53’ dry box van s . 8 The agencies used the results from the on - road testing of 53’dry box vans to assist in develop ing a erodyn amic standards for the trailer ty pes covered under this proposed rulemaking. Specificall y, the delta C d A for trailers configured with various devices will be used to determine categories of values for GEM input; as discussed further under Section 3.2.7 . Although all of the on - road testing for different trailer ty pes is not complete at the time of proposal , we do have data on other trailer ty pes using alternate aerodynamic methods (e.g., red uced - scale wind tunnel) and discussed further below . Therefore, the combination of existing, on - road and alternate method data on other trailer ty pes is a good foundation to develop aerodynamic standards for other trailer types. Further, we believe the r esults of future on - road testing will be consistent with the trends emerging from the existing data . Once all testing is complete, a full report will be included in the docket and further considered in the context of the trailer aerodynamic standards . 

### 3.2.5.2 **Red uced**  **- Scale**  **Wind Tunnel Testing of Different Trailer OEMs,**  **Configurations, and Trailer**  **Types** In addition to the on - road coastdown and constant speed procedures presented previousl y, we are proposing to allow additional aerodyn amic assessment methods (e.g., wind tunnel, CFD) to generate delta C d A values for the HD Phas e 2 trailer program . In contrast to the on - road test procedures, the wind tunnel provides a stable , controllable environment yi elding a more repeatable test and allows for more accurate measurement of the aerodyn amic impact of tractor trailer modifications. In addition, wind tunnels provide testers with the ability to yaw the vehicle in a controlled, specific manner at positive and negative angles relative to the original centerline of the vehicle to accurately capture the influence of non - uniform wind direction on the C d (e.g., wind averaged C d). Most trailers in the U.S. are 28 ’ or longer and the agencies are not aware of***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 30 any viable, available wind tunnels that can accommodate full scale tractor - trailer combination vehicles . As a result, we exclusively used reduced - scale wind tunnel (RSWT) testing to support the HD Phase 2 aerodynamic assessment rather than a mix o f full scale wind tunnel (FSWT) and RSWT testing as performed in HD Phase 1. F or HD Phase 2, we are proposing to carry over the use of SAE J1252 with the exceptions and modifications noted above. In addition, since the finalization of HD Phase 1, SAE J12 52 has been updated and we are incorporating b y reference the most recent version for HD Phase 2. For HD Phase 2, we are performing wind tunnel testing to inform revisions to the standard trailer test article for the tractor program and to develop separat e trailer standards. The RSWT testing was performed at the Automotive Research Center (ARC) in Indianapolis Indiana. The ARC wind tunnel is a closed single return tunnel with 3/4 open - jet working section and moving ground plane (2.3 m wide x 2.1 m high x 5.5 m long (7.5 ft x 6.8 ft x 18 ft)). It is powered by an air - cooled 373kW (274 hp) variable speed DC motor that drives a 9 - bladed fan with carbon fiber blades. It s speed may be varied and set at any

value from 0 to 610 rpm. The maximum wind speed is about 50 m/s (164 ft/s). The wind tunnel can accommodate a model up to 50 percent scale (1/2 scale) for race car applications down to 12.5 percent scale (1/8 th scale) for Class 8 tractor and trailer combinations. The wind tunnel is equipped with a movin g ground plane ( i.e. , rolling road), four - stage boundary layer suction sy stem, and a top - mounting “Sting” s ys tem that allows for yawing of the model. For model development, ARC has in - house model developers and can create highly detailed scale models usin g original computer aided design and engineering (CAD/CAE) drawings or using in - house scanning equipment to perform scanning and digitizing to create CAD/CAE drawings (see Figure 3 - 6 below).***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 31 **Figure 3**  **- 6**  **1/8th s**  **cale t**  **ractor -**  **t railer**  **m odel in ARC**  **r educed**  **s cale**  **w ind**  **t unnel.** ***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 32 The RSWT testing was conducted simulating an actual vehicle speed of 65 miles per hour (mph) using a tunnel speed of 111.8 mph and Reynolds number ( Re ) of greater than one million (1x10 6 ) on one eighth scale models of heav y- duty, Class 8 sleeper and day cab tractors equipped with the full aerodynamics pack age components sold on the full size version of the tractor ; consistent with our HD regulatory requirements . F or our test program, we assumed a base tractor - trailer gap of 45 inches and a bogey position of 40 feet (California position) from th e leading edge of the trailer. To support HD Phase 2, we tested the latest model year tractor available from each of the four tractor OEMs in sleeper cab form and one tractor OEM in day cab form. The tractor models used in the RSWT matched the tractor m odels used for the on - road testing to the extent feasible. For one manufacturer , we were not able to match the exact tractor model but did test model s from that OEM in the RSWT and on - road. While the results across the tractor models are not directly comparable, the data provides some representativeness of the expected performance from that OEM’s tractors. In addition, we also tested three 53 foot dry box van trailers from three different trailer OEMs: Wabash, Great Dane, and Hy undai Translead; to evaluate aerodynamic trailer devices. For aerodynamic trailer devices, we focused on technologies that may improve areas on the tractor - trailer where large amounts of aerody namic drag can occur and tested: one OEM trailer front treatment (e.g., front end trailer gap reduction device), two OEM side treatments (e.g., trailer side skirts) and one OEM aft treatment (e.g., trailer boat tail). In the case of the trailer side skirts and boat tail, a portion of the trailer devices used in the RSWT matched those used fo r the on - road testing. Thus, we ensured some overlap between the RSWT and on - road testing , although we were able to test a broader range of trailer devices . Below in Table 3 - 10 are the RSWT results for the various configurations of four OEM sleeper cabs, one OEM day cab, three OEM 53 - foot dry box van trailers, and four aerodynamic trailer devices ( two trailer skirts, one rear boat tail, one front trailer gap reducer) ; averaged across trailer OEMs. The variation across the three OEM 53 - foot dry box van trailers was small and should be considered negligible at 1.0 percent on average . The variation range d from 0.5 to 0.9 percent for three of the four sleeper cab tractors and the day cab and a high of 2.3 percent for one of the four sleeper cab tractors. Where there were multiple runs on the same tractor, trailer, and device, the results were averaged across those runs and then i ncluded in the overall average.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 33 **Table 3**  **- 10**  **Results o**  **f Reduced -**  **Scale Wind Tunnel Tes ting to Assess Tractor Trailer**  **Perform ance**  **w ith**  **Various Aerodynamic Trailer Devices.** CAB TYPE ROOF

HEIGHT CONFIGURATION C **d** A [ m2 ] DELTA C **d** A (VS. STANDARD) % DELTA C **d** A (VS. STANDARD) Sleeper 1 High Standard 5.425 -- -- With Trailer Skirt #1 5.002 0.423 7.8% With Trailer Skirt #2 4.914 0.511 9.4% With Boat Tail 5.085 0.340 6.3% With Trailer Gap Reducer 5.450 - 0.024 - 0.5% With Trailer Skirt #2 and Boat Tail 4.453 0.972 17.9% With Trailer Skirt #2, Boat Tail, and Trailer Gap Reducer 4.460 0.965 17.8% Sleeper 2 High Standard 5.556 -- -- With Trailer Skirt #1 5.054 0.586 10.5% With Trailer Skirt #2 4.962 0.594 10.7% With Boat Tail 5.191 0.365 6.6% With Trailer Gap Reducer 5.5 65 - 0.020 - 0.4% With Trailer Skirt #2 and Boat Tail 4.464 1.092 19.6% With Trailer Skirt #2, Boat Tail, and Trailer Gap Reducer 4.449 1.106 19.9% Sleeper 3 High Standard 5.622 -- -- With Trailer Skirt #1 5.145 0.477 8.5% With Trailer Skirt #2 5.056 0.566 10.1% With Boat Tail 5.305 0.318 5.6% With Trailer Gap Reducer 5.632 - 0.009 - 0.2% With Trailer Skirt #2 and Boat Tail 4.566 1.056 18.8% With Trailer Skirt #2, Boat Tail, and Trailer Gap Reducer 4.560 1.062 18.9% Sleeper 4 High Standard 5.5 63 -- -- With Trailer Skirt #1 5.0 79 0.481 8.7% With Trailer Skirt #2 5.003 0.557 10.1% With Boat Tail 5.2 29 0.332 6.0% With Trailer Gap Reducer 5.5 47 0.015 - 0.3% With Trailer Skirt #2 and Boat Tail 4.4 36 1.121 20.2% With Trailer Skirt #2, Boat Tail, and Trailer Gap Reducer 4.4 45 1.112 20.1% Day High Standard 5.609 -- -- With Trailer Skirt #1 5.353 0.256 4.6% With Trailer Skirt #2 5.298 0.311 5.6% With Boat Tail 5.240 0.370 6.6% With Trailer Gap Reducer 5.596 0.014 0.2%***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 34 With Trailer Skirt #2 and Boat Tail 4.910 0.699 12.5% With Trailer Skirt #2, Boat Tail, and Trailer Gap Reducer 4.902 0.707 12.6% We believe that most trailers in the U.S. fleet will adopt some aerodyn amic technologies by 2021. W e are proposing to revise the standard trailer definition for 53 - foot air ride dry box van trailers to include aerody namic trailer devices. Specificall y, we are proposing trail er skirts as part of the standard configuration for tractor aerody namic evaluation. We are u sing the results in Table 3 - 10 , to inform the proposed tractor aerody namic bin categories for use as GEM inputs. In addition to evaluating the aerodyn amics of 53 foot dry box vans in the RSWT, we also evaluated the aerodyn amics of shorter, 28 foot dry box van trailers , singular or in tandem/dual/twin configuration , known as “pup ” trailers. This testing was performed using a single - axle, day

cab tractor using similar trailer devices (e.g., trailer skirts, rear boat tail, and front trailer gap reducer) with a tractor - to - first trailer gap of 44 inches and a first pup - to - second pup trailer gap of 48 inches. Table 3 - 11 shows the results of this testing for the configurations tested: **Table 3**  **- 11**  **Resul ts**  **o f Reduced**  **- Scale Wind Tunnel Testing**  **t o Assess Tractor Trailer Perform**  **ance w**  **ith Various Aerodynamic Trailer Devices**  **.** DUAL PUP TRAILER RESULTS Configuration C d A [m 2 ] Delta C d A (vs. Standard) % Delta C d A (vs. Standard) Standard 6.022 -- -- Skirt on First Trailer Only 5.902 0.120 1.99% Skirt on Second Trailer Onl y 5.735 0.286 4.76% Skirt on Both Trailers 5.586 0.436 7.24% Skirt and Gap Reducers on Both Trailers 5.289 0.733 12. 2 % Skirt and Gap Reducers on Both Trailers w/ tail on second trailer 5.208 0.814 13.5%

SINGLE PUP TRAILER RESULTS Standard 5.384 -- -- Skirt on Trailer 5.226 0.159 2.95% Skirt and Gap Reducer on Trailer 4.971 0.414 7.68% Based on the results in Table 3 - 11 above, the potential to significantly improve the aerodynamic performance of pup trailers, singular or in tandem/dual/twin, exists using various***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 35 trailer devices. The maximum package of trail er side skirts on both trailers, gap reducers on both trailers, and a boat tail on the second trailer produced a benefit of 13.5 percent over the standard dual pup trailer configuration. However, since pup trailers may be frequently interchanged (e.g., dro p off the second pup trailer or both pup trailers at one destination; proceed to the next destination to pick up a new first pup trailer, second pup trailer or both pup trailers) , the most practical application may be dual pup trailers with just trailer si de skirts and gap reducers on both trailers . The presence of boat tail/aft treatment restricts that trailer to a second/rear position, depending on the length of the aft trailer device , and omitting this device allows for pup trailer sy mmetry . Even with the omission of an aft trailer device , the trailer side skirts an d gap reducers on both trailers configuration still achieves a benefit of 12. 2 percent . Notwithstanding, the added use of aft trailer devices; with proper consideration for the length of the device to accommodate operational constraints versus the potential tradeoff in aerodyn amic performance with reduced, aft trailer device length; should be investigated further to identify additional dual pup trailer optimization. Installing skirts/gap redu cers on both trailers for dual pup trailer configurations also produces benefits from the use of a single pup trailer with trailers side skirts and gap reducer; achieving a benefit of 7.68 percent versus the standard, single pup trailer without any devices. There may

be occasions where a dual pup tractor - trailer must travel between destinations in single pup trailer configuration. Thus, the presence of trailer side skirts and gap reducers on both pup trailers also aids the aerodynamic performance for the occasions where it is operated in a single pup trailer configuration . Finally , we also evaluated the impact of aerody namic devices on reefer trailer performance. Reefer trailers are similar in b asic shape to 53 - foot dry box van trailers, but are equipped with a thermal refrigeration unit (TRU) on the front of the trailer. Thus, the TRU fills the gap space between the tractor - trailer where gap reduction technology would normally

be fitted. In ad dition, based on conversations with reefer trailer manufacturers, although reefer trailers are less prevalent in the field, they tend to see much more operation than the ty pical 53 - foot dry box van trailer due to their smaller numbers (1.5 - 2.2 to 1 for tra ctor to reefer trailer ratio versus 3 to 1 for conventional 53 - foot dry box van trailers). As such, there is more opportunity to realize the benefits from optimizing reefer trailers.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 36 **Table 3**  **- 12**  **Results o**  **f Reduced**  **- Scale Wind Tunnel Tes**  **ting of Reefer Trailer Using a 2012 Model Year**  **Tractor** CONFIGURATION C D A (ZERO YAW) [ m2 ] DELTA C **d** A FROM STANDARD REEFER (% DELTA) DELTA C **d** A VS . STANDARD DRY BOX VAN TRAILER FROM THE SAME TRAILER OEM % DELTA (VS . STANDARD TRAILER) Standard Reefer 5.840 -- - 0.264 - 4.7% Skirt Only 5.141 0.699 (12.0%) - 0.196 - 4.0% Boat tail only 5.607 0.232 (4.0%) - 0.448 - 8.7% Skirt +Boat Tail 4.596 1.244 (21.3%) - 0.114 - 2.5% V s . OEM standard trailer w/ Skirt + Boat Tail + Gap -- -- - 0.146 - 3.3% T he results in Table 3 - 10 , Table 3 - 11 , and Table 3 - 12 will also be used to support the newly proposed, trailer regulations. Specificall y, the delta C d A for trailers configured with various devices will be used to determine categories of values for GEM input ; as discussed further in Section 3.2.7 . 

### 3.2.6 **Standardized Trailer Definitions for Heavy -**  **Duty Tractor**  **Testing** In HD Phase 1, we finalized the use of a model input (i.e ., an input to GEM at certification) reflecting a standardized trailer for each subcategory of the Class 7/8 tractors based on tractor roof height. The height of the roof fairing is designed to minimize the height differential between the tractor and ty pical trailer to reduce the air flow disruption. L ow roof tractors are designed to carry flatbed or low - boy

trailers. Mid roof tractors are designed to carry tanker and bulk carrier trailers. High roof tractors are designed to optimally pull box trailers. However, we recognize that during actual operation tractors sometimes pull trailers that do not provide the optimal roof height that matches the tractor. In order to assess how often tractor and trailer mismatches are found in operation, EPA conducted a study based on observations of traffic across the U.S. 9 Data was gathered on over 4,000 tractor - trailer combinations using 33 live traffic cameras in 22 states across the United States. Approximately 95 percent of tractor s were “matched”

– i.e. optimized

– per our definition ( e.g. box trailers were pulled by high roof tractors and flatbed trailers were pulled with low roof tractors). The amount of mismatch varied depending on the type of location. Over 99 percent of the tractors were observed to be in matched configuration in Indiana at the I - 80/I - 94/I - 65 interchange, which is representative of long - haul operation. On the other hand, onl y about 90 percent of the tractors were matched with the appropriate trailer in metro New York City , where all mismatches consisted of a day cab and a tall container trailer. The study also found that approximately 3 percent of the tractors were trave ling without a trailer or with an empty flatbed. The agencies therefore concluded in Phase 1 that given this very

limited degree of mismatch, it is reasonable to use a standardized definition which optimizes tractor - trailer matching. For purposes of comp liance testing, the agencies also finalized bob - tail testing for low roof and mid roof tractors to facilitate repeatability and reproducibility

of test data in response to concerns raised by tractor manufacturers.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 37 Recently , trailer OEMs and aftermarket manufacturers have begun implementing new aerodynamic technologies on box trailers, to improve their aerodynamic efficiency and to lower overall tractor - trailer fuel consumption. There are a range of technologies to affix to the front (e.g., nose cones, gap reducers, front lip devices); sides and underbody (e.g., skirts, wedge shaped devices aft of trailer landing gear and fore of trailer rear axles/bogey s); top (e.g., vortex generating devices to promote turbulent flow and delay boundary

layer separation along the length of the trailer) and rear (e.g., tails, rear lip spoilers and diffusers) of the trailer. However, the most widely

implemented devices in the market today are trailer side skirts that extend in the gap between the fifth wheel and the trailer bogey to restrict underbody air flow and subsequent drag and rear/aft trailer treatments extending from the rear of the trailer (e.g. , boat tails, that reduce the low pressure region, and associated, subsequent drag, on the rear of the tractor trailer) . As discussed in Section III . E(2)(a)(iii) and Section IV . D(2) of the preamble, we estimate that approximately

50 percent of the new trailers sold in 201 8 will have trailer side skirts. 10 , 11 As the agencies are propo sing tractor standards for model year 2021 and beyond, we believe that it is appropriate to update the standardized box trailer definition to reflect the technologies we project will be used on the majority of the trailers in the fleet during that timefram e . Therefore, we are proposing for Phase 2 that the standardized box trailer used for tractor certification be updated to include a trailer skirt starting in model year 2021 . Although we are proposing GHG standards for trailers that capture the drag area improvement for various trailer devices, including trailer skirts, beginning in model year 2018, this proposed update to include a test article to the standardized trailer is strictly for the purpose of certifying tractors beginning in model year 2021 , an d is not related to the proposed trailer GHG standards themselves . Based on the test results shown above in Table 3 - 10 , Table 3 - 11 , and Table 3 - 12 and comments from stakeholders, the agencies have chosen to update the test article specifications for 53’ dry

box van trailers below in Table 3 - 13 . Specificall y, the s tandardized, 53’ air ride dry v an t est article we are proposing for Phase 2 will include trailer side skirts on the standardized trailer for tractor aerodyn amic assessment . We propose that the skirt meet the dimensions shown in Table 3 - 13 based on the devices used for the agencies’ aerodyn amic assessment , accounting for potential design, differences, variations and tolerances for other trailer attributes (e.g., landing gear overlap, rear bogey clearance, ground clearance) . Trailer side skirts that do not meet the size specifications (e.g., length and width) below can be used , with prior approval from the agencies , on the standardized trailer used for the aerodyn amic assessment of tractors , provided that they do not exceed the dimensions in Table 3 - 13 but are no shorter than 270 inches ± 4 inches in length when measured along the top edge of the trailer side skirt; and meet all other specifications for positioning on the trailer; except for the distance from the front and rear trailer edge which may

vary based on a shorter skirt length . Finally , the tractor must be a stock OEM tractor without additional devices installed, unless devices are included as part of a stock OEM aero package (e.g., drive axle wheel covers, fairings or fenders).***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 38 **Table 3**  **- 13**  **53’ D**  **ry Box**  **Van Trailer Test Article**  53’ AIR RIDE DRY BOX VAN TRAILER Length: 53 feet (636 inches ; 1615.44 cm) ± 1 inch Width: 102 inches ± 0.5 inches Height: 102 inches (162 inches or 13 feet, 6 inches (+0.0 inch/ - 1 inch) from the ground) Capacity: 3 , 800 cubic feet Assumed trailer load/capacity: 45,000 lbs Suspension: Any (see “trailer ride height” below) Corners: Rounded with a radius of 5.5 inches ± 0.5 inches Bogie/Rear Axle Position: Tandem axle (std), 146 inches ± 4 .0 inches from rear axle centerline to rear of trailer. S et to California position . Skin: Generally smooth with flush rivets Scuff band: Generally smooth, flush with sides (protruding ≤ 1/8 inch) Wheels: 22.5 inches. Duals . Std mud flaps . Doors: Swing doors . Undercarriage/Landing Gear: Std landing gear, no storage boxes, no tire storage, 105 inches ± 4.0 inches from front of trailer to centerline of landing gear Underride Guard Equipped in accordance with per 49 CFR 393.8 6 Aerodynamic Trailer Device Type: Trailer Side Skirt s Aerodynamic Trailer Device Specifications Applicable to Trailer Side Skirts : Skirts must be installed on both sides of the trailer Skirts must be designed to fit between the landing gear and the rear bogey, in the most forward position (California), of the trailer and must be: 118 inches ± 4 inches measured from the front of the trailer to the leading, forward - most point of the upper/top edge of the skirt Skirts must be straight and flush with the trailer sides Skirts must be: 341 inches, ± 4 inches in total length , measure d along the top/upper edge T he same total length on the bottom/lower edge as the top /upper edge ( e.g., rectangular in shape ) but shall be no less than 268 inches ± 4 inches in length along the bottom edge (e.g., angled front/rear edge or front edge only) 36 inches ± 2 inches in total width , measured between the top/upper and bottom/lower edge , at the midpoint of the skirt Skirts may minimally (e.g., 10% or less) overlap the trailer landing gear at the forward - most point along the upper/top edge but should not cover the trailer landing gear with any portion of the skirt leading/front edge (e.g., skirt may not extend forward beyond the landing gear position Tires f or the Standard Trailer and the Tractor: a. Size: 295/75R22.5 or 275/80R22.5 b. C rr<5.1 kg/metric ton c. Broken in per S ection 8.1 of SAE J1263 d. Pressure per S ection 8.5 of SAE J1263 e. No uneven wear f. No re - treads g. If these tires or appropriate Smart Way tires are un available, the Administrator testing may include tires***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 39 used by the manufacturer for certification. Test Conditions: Tractor - trailer gap: 45 inches ± 2.0 inches. King pin setting: 36 inches ± 0.5 inches from front of trailer to king pin center line. Trailer ride height: 115 inches ± 1.0 inches from top of trailer to fifth wheel plate, measured at the front of the trailer, and set within trailer height boundary from ground as described above. Mud flaps: Positioned immediately following wheels of last axle . **For special cases in which a trailer would be used for coastdown testing for m id**  **- roof and low**  **- roof tractors,**  **the specifications for the tanker and flatbed trailers are being carried over fro**  **m HD**  **Phase 1, and are shown**  **, unchanged,**  **in Table**  **3 -**  **14 and**  Table 3 - 15 below , respectively .

**Table 3**  **- 14**  **Tanker Trailer Specifications f**  **or Special Testing** TANKER TRAILER Length: 42 feet ± 1 foot, overall 40 feet ± 1 foot, tank Width: 96 inches ± 2 Height: 140 inches (overall, from ground) Capacity: 7,000 gallons Suspension: Any (see “trailer ride height” below) Tank: Generally cylindrical with rounded ends. Bogie: Tandem axle (std). Set to furthest rear position. Skin: Generally smooth Structures: (1) Centered, manhole (20 inch opening), (1) ladder generally centered on side, (1) walkway (extends lengthwise) Wheel fairings: Wheels: 24.5 inches. Double wide. Tanker Operation Empty **Table 3**  **- 15**  **Flatbed Trailer Specifications**  **f or Special Testing**  FLATBED TRAILER Length 53 feet Width 102 inches Flatbed Deck Heights: Front: 60 inches ± 0.5 inch es Rear: 55 inches ± 0.5 inch es Wheels / Tires 22.5 inch diameter tire with steel or aluminum wheels Bogie Tandem axles, may be in “spread” configuration up to 10 feet ± 2 inches. Air suspension Load Profile: 25 inches from the centerline to either side of the load; Mounted 4.5 inches above the deck. Load height 31.5 inches above the load support. Trailer should be empty.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 40 The regulations in 40 CFR 1037.501 prescribe the standardized trailer for each tractor subcategory

(low, mid, and high roof) including trailer dimensions based on the tables above . 

### 3.2.7 **Standardized Tractor**  **Definition for Heavy**  **- Duty**  **Trailer Testing**  Similar to the standardized trailer definition for tractor aerodynamic assessment, the agencies are proposing to define a standardized tractor definition for trailer aerody namic assessment. The proposed standardized tractor definition is based on tractor attributes such as a Class 8, high roof, tandem axle tractor equipped with, at a minimum, a roof fairing, cab side extenders and fuel tank/chassis skirts . This ty pe of tractor ty

pically meet s a Bin III or better tractor aerodynamic level under HD GHG Phase 1 and is expected to meet the proposed Bin III level for HD GHG Phase 2 . We believe the majority of tractors in the U.S. trucking fleet will be Bin III or better in the timeframe of this rulemaking and trailer manufacturers have the option to c hoose higher - performing tractors in later ye ars as tractor technology improves. As with the standardized trailer’ s test article specification, the aerodynamic specification for the standardized tractor here is strictl y for the purpose of certifying trailers beginning in model year 2018 model ye ar. Therefore, although the aerodyn amic level of the standardized tractor for trailer certification potentially

overlaps with tractors designed to meet the 2021 and beyond tractor GHG standards, it is only intended to serve as a specification for trailer certification to the 2018 and beyond trailer GHG standards. Accordingl y, we are proposing that trailer manufacturers would use this standardized tractor definition with their trailers to conduct A to B testing to capture the delta C d A for their trailers that are either: equipped with aerodynamic devices to meet the proposed trailer standards or are designed to be more aerodyn amic than current, standard trailers . Sp ecificall y, the trailer manufacturers would use the standardized tractor to generate A to B test values where the “A” represents a standard test and “B” represents the modified/advanced trailer; both tests performed using the same standardized tractor. S ubsequently , the tract or manufacturer would input their trailer OEM - specific delta C d A value in the GEM model and the model would determine the appropriate, default trailer delta C d A GEM value; where the default delta C d A GEM value is based on the test res ults in Section s 3.2.5.1 and 3.2.5.2 above. This value is applied to a default tractor /trailer C

d A value based on a Bin III or greater Class 8 sleeper cab tractors with a standard trailer. Finally, the default tractor/trailer C

d A value with the default trailer C d A value applied would be used to determine the greenhouse gas emissions for this configuration by the GEM model . For trailer OEMs that are certifying a trailer where devices are added to an existing OEM trailer design, the trailer used for both “A” and “B” test uses a trailer meeting our standardized trailer definition for 53’ air ride dry box vans shown above in Section 3.2.6 , Table 3 - 13 , without any trailer devices installed; with the same standard referenc e tractor used for both tests. In contrast, for trailer OEMs that certify a completely

new trailer design, the “A” test uses a trailer meeting our standardized trailer definition for 53’ air ride dry box vans shown above in Section 3.2.6 , Table 3 - 13 , without any trailer devices installed and the “B” test would be the new, OEM trailer design; with a standard r eference tractor used for both tests. In summary , the standard reference tractor would be used for all trailer OEM “component” level***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 41 testing; where the “component” in the B test can range from an add - on trailer device up to a completely

different trailer design. To assist in defining the standardized tractor for different trailer types, below are the proposed trailer sub - categories used for GEM from Chapter IV of the preamble . **Table 3**  **- 16**  **Description of Baseli ne Tractor**  **- Trailers Used In GEM**  **from Section**  **IV .**  **D(2)(b)(ii), of the Pream** **ble** TRAILER SUBCATEGORY FEATURES Dry v an 50 feet and shorter Class 8 high roof day cab, pulling solo 28’ dry van C d A = 6.1 , Crr = 6.0 kg/ton Dry v an longer than 50 feet Class 8 high roof sleeper cab pulling a solo 53’ dry van C d A = 6. 2 , Crr = 6.0 kg/ton Refrigerated v an 50 feet and shorter Class 8 high roof day cab pulling a solo 28’ ref van C d A = 6. 0 , Crr = 6.0 kg/ton Refrigerated v an longer than 50 feet Class 8 high roof sleeper cab pulling a solo 53’ ref van C d A = 6. 1 , Crr = 6.0 kg/ton Based on this table , we are propos in g standardized tractor definition s based on tractor ty pe and attributes that reflect the types of tractors used for trailers in each of these subcategories. Specificall y, we are proposing that all tractors for all trailers greater than 50 feet shall use a standardized tractor meeting the following criteria for A to B testing : a Class 8, high - roof sleeper cab, tandem axle tractor that meets HD Phase 2 Bin III or better Class 8 high roof sleeper cab tractor aerody

namic standards. For all trailers less than 50 feet, a standardized tractor meeting the following criteria shall be used for A - B testing: Class 8 , high - roof day cab, dual axle tractor that meet s HD Phase 2 Bin III or better Class 8 high roof day cab tractor aerody

namic standards.

**Table 3**  **- 17**  **Characteristics of Standard Tractor for Aerodynamic Assessment of**  **Trailers** BOX TRAILERS 50 FEET AND LONGER CLASS 8 HIGH ROOF SL EEPER CAB DUAL - AXLE BIN III OR BETTER TRACTOR, C D A < 6.5 CAB SIDE EXTENDERS FUEL TANK COVER/ CHASSIS SKIRTS ROOF FAIRING Box trailers shorter than 50 feet Class 8 high roof day cab Dual - axle Bin III or better tractor, C d A < 6.7 Cab Side extenders Fuel tank covers/ Chassis Skirts Roof Fairing***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 42 

### 3.2.8 **Continued Use of the Aerodynamic**  **Alterna t**  **e Method Factor ( F**  **alt -**  **aero** 

### ) for **HD Phase 2**  **Tractors** As the agencies showed in Phase 1, aerodyn amic test method s differed in their prediction s of drag coefficient . 12 O n - road methods , such as coastdown and constant speed tests, are performed in uncontrolled real - world environments, whereas wind tunnel testing is performed in constrained, controlled conditions , and CFD is a simulation that attempt s to repl icate complex aerodynamic events. Different test methods have differences with regards to environmental conditions, assumptions for non - aerody namic drag forces, tunnel geometry , boundary conditions, and simulation characteristics . These differences can le ad to different results, even though they are used to measure or calculate the same parameter. The agencies acknowledge d that there will never be perfect alignment between the predicted drag area values from the aerodynamic methods even with full, appropri ate correction for every factor , but wanted to allow the use of these methods, which are currentl y being used by the manufacturers, to limit test burden for certification As a result, for HD Phase 1, we employed the use of an aerodynamic method adjustment factor (or F

alt - aero ) factor, to relate the results from the reference method , a coastdown test, to the results from the alternative method as a ratio of the coastdown r esult to the alternate method result for selected Class 8 high roof sleeper cab . T he F alt - aero is then multiplied to the results generated using the alternative method for all other OEM configurations This allowed manufacturers the convenience and lower test burden of using existing aerody namic protocols rather than pursuing extensive data correction to produce equivalent results across the aerodynamic methods. For HD Phase 2, we are proposing to continue to allow the use of data from alternate aerodynamic test methods , and subsequentl y the aerodynamic method adjustment factor. Thus, for H D GHG Phase 2, we explored the level of agreement between the aerody namic methods similar to HD GHG Phase 1. The method comparison was used in HD GHG Phase 1 to demonstrate that for a given tractor and trailer model with specified conditions for each of t he methods, testing meeting these specifications performed with the required level of precision (e.g., repeated with a low level of error) could yield a reasonable level of agreement across the aerodynamic method. Consequently , there is no guarantee that the same level of agreement would be produced using different facilities, conditions, or test articles . However, a lthough this level of agreement is only applicable for that tractor and trailer model using the specified conditions for those tools in a specific facility , this data was sufficient to demonstrate the level of agreement possible and support the use of specified conditions in HD GHG Phase 1 (as shown in Figure 3 - 7 a and b ) .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 43 **These trends were**  **similarly observed**  **in the HD GHG Phase 2 data.**  **Accordingly, below in**

Figure 3 - 7 a is the aerodynamic method co mparison using HD Phase 2 test results. The results are shown are for three of the four Class 8, high roof, sleeper cab tractors from coastdown, constant speed and zero degree C d A RSWT testing; normalized to the coastdown results. The data in Figure 3 - 7 a is presented using the zero yaw C d values for the reduced scale wind tunnel (RSWT) and the constant speed test results normalized to the coastdown test results (e.g., RSWT or constant speed results divided b y the coastdown result) similar to the comparison used for HD GHG Phase 1 for a standard trailer . The HD GHG Phase 2 data shows a similar level of method agreement as HD GHG Phase 1 for the coastdown test and RSWT (constant speed testing was not performed for HD GHG Phase 1).

1.00 1.00 1.00 1.03 0.95 0.97 0.92 0.90 0.93

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Sleeper 1 Sleeper 2 Sleeper 3 Coastdown Constant Speed RSWT (Cd*A @ zero yaw)***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 44 **Figure 3**  **- 7**  **a Met**  **hod Comparison for Coastdown, Constant Speed and RSWT ( Zero**  **- Yaw**  **C d** **) Testing Norm**  **alized to the Coastdown Results for Class 8 High Roof Sleeper Cab Tractors and Standard Trailers**  **following a HD GHG Phase 1 approach .**  **( Note: T**  **he results of Sleeper 1 and Sleep er 3 are not directly**  **com parable since the test articles do not m**  **atch but are shown to represent**  **the overall**  **industry trend given a**  **manufacturer’s fleet variance**  **. )**  1.00 1.00 1.00 1.03 0.95 0.97 0.92 0.90 0.93

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Sleeper 1 Sleeper 2 Sleeper 3 Coastdown Constant Speed RSWT (Cd*A @ zero yaw)***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 45 It is interesting to not e that if the WAC d concept had been adopted in HD GHG Phase 1, the level of method agreement, and consequentl y the Falt - aero factor used to characterize and account for method inequality , may have been closer to parity (e.g., Falt - aero closer to 1) based on the HD GHG Phase 2 WAC d data for a standard trailer , as shown in Figure 3 - 8 b below.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 46 **Figure 3**  **- 8**  **b Method Com parison for Coastdown,**  **Constant Speed and RSWT (WACdA @ 55 mph w/ 7 m ph**  **wind) Testing Norm**  **alized to the Coastdown Results for Class 8 High Roof Sleeper Cab Tractors and**  **Standard Trailers .**  **This approach was recommended by comm enters for HD GHG Phase 1. (**  **Note: The results of**  **Sleeper 1 and Sleeper 3 are not directly com parable since the test articles do not m**  **atch but are**

**shown to represent the overall industry trend given a manufacturer’s fleet variance. )**  1.00 1.00 1.00 1.03 0.95 0.97 1.025 1.033 1.035

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Sleeper 1 Sleeper 2 Sleeper 3 Coastdown Constant Speed RSWT (Cd*A @ zero yaw)***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 47 For HD GHG Phase 2, we are proposing to include the wind average drag and will discuss this i n Section 3.2.9 . Further, we will revisit the method comparison with the inclusion of wind average drag for a trailer equipped with side ski rts; consistent with the proposed HD GHG Phase 2 approach. 

### 3.2.9 **Wind -**  **Averaged Drag Area**  **and General Aerodynamic Assessment Results Based on Proposed**  **HD Phase 2**  **Tractor Modifications**  For HD Phase 2, we are proposing to use the WA C d A as the main GEM input (Secti on 3.2.3 ), revise the standard reference trailer for tractors ( Chapter 3.2.6 ), and continue to use a F alt aero when alternative aerody namic methods are used for certification and compliance demonstration ( Chapter 3.2.8 ). Based on the proposed modifications, this section uses the HD Phase 2 WAC

d A results from RSWT testing for a tractor - trailer combination with trailer side skirts installed to demonstrate th e coastdown yaw sweep shift concept, calculation of the alternate method factor (F alt - aero ) , and provide a cross - method comparison for illustrative purposes . To begin, below in Table 3 - 18 are the values for the zero yaw drag areas ( C d A (zero)) and WAC d A at 55 miles per hour (mph) for each sleeper cab tractor an d 53’ trailer, averaged across three OEM trailers with trailer side skirt #2 installed on the trailer. **Table 3**  **- 18**  **Ze ro Yaw and Wind Average Drag**  **Area RSWT Results**  **for Tractor**  **- Trailer Com** **binations with a Trailer Side Skirt**  **(Res ults for Trailer Side Skirt #2**  **S hown)**  **.** TRACTOR C d A (ZERO) C

d A DELTA VS. STANDARD TRAILER C d A % DELTA VS. STANDARD TRAILER WA C d A (@ 55 MPH) WAC d A DELTA VS. STANDARD TRAILER WAC d A % DELTA VS. STANDARD TRAILER WAC D A

– C D A DELTA ( WAC D A OFFSET) WAC D A

– C D A % DELTA (VS. C D A ) Sleeper 1 4.914 0.511 9.42% 5.419 0.624 10.33% 0.505 10.27% Sleeper 2 4.962 0.594 10.68% 5.705 0.700 10.94% 0.742 14.96% Sleeper 3 5.056 0.566 10.07% 5.598 0.687 10.93% 0.542 10.73% Sleeper 4 5.003 0.560 10.07% 5.627 0.714 11.26% 0.625 12.49% Day 5.298 0.311 5.55% 5.755 0.612 9.61% 0.457 8.63% Sleeper Average ( 2 out of 4 tractors w/ matching coastdown data) 4.9 38 0.55 2 10.1% 5.5 62 0.6 62 10. 6 % 0. 624 12. 6 %

Based on the results in Table 3 - 18 , there is good alignment in the data ( C d A standard deviation of 0.06, 1.21 percent relative standard error; WA C d A standard deviation of 0.12, 2.16 percent relative standard deviation) across sleeper cab tractors and trailers equipped with trailer side skirts (e.g., a similar trend was demonstrated in the data for trailer side skirt #1 as well).***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 48 **Similar to the m ethod comparison**  **in**

Figure 3 - 7 for zero degree drag area and a standard trailer , Figure 3 - 9 below shows the WAC d A method comparison for three of the four Class 8, high roof, sleeper cab tractors with a trailer equipped with trailer side skirts consistent with the proposed HD GHG Pha se 2 reference trailer modifications . The results are shown for constant speed testing and WA C d A RSWT testing at 55mph assuming a 7mph wind speed, normalized to the coastdown test results. As discussed above, these results are for a specific set of tract or - trailer models, specifications and facilities for those tools and, thus, a similar or equivalent level of agreement is not guaranteed for using different criterion. However, as shown for HD GHG Phase 1, there is a certain level of agreement achievable using set conditions for a given tractor - trailer model as proposed under HD GHG Phase 2. This is prior to any

adjustment of the coastdown result to incorporate wind averaging which would theoretically increase the coastdown values upward since the wind ave rage drag area is higher than zero degree yaw drag area. However, this is a useful comparison to demonstrate how the use of wind average drag in HD GHG Phase 1 may have influenced the level of agreement between the methods, and the resulting OEM Falt - aero values (e.g., Falt - aero values closer to 1), versus the use of zero yaw drag adopted in HD GHG Phase 1. We will explore the method comparison further with the inclusion of wind average drag later in this section. 1.00 1.00 1.00 1.03 0.95 0.97 0.92 0.90 0.93

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Sleeper 1 Sleeper 2 Sleeper 3 Coastdown Constant Speed RSWT (Cd*A @ zero yaw)***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 49 **Figure 3**  **- 9**  **Unadjusted Method Comparison for Coastdown, Constant Speed and RSWT (WACdA**  **@ 55 mph**  **w/ 7 m ph wind**  **) Testing Normalized**  **to the Coastdown Re sults, for Class 8 High Roof Sleeper Cab Tractors**  **and Trailers Equipped with Trailer Side Skirts .**  **Note: The results of Sleeper 1 and Sleeper 3 are not directly com** **parable since the test articles do not m atch but are shown to represent overall industry tre**  **nd given a manufacturer’s unique fleet.**  1.00 1.00 1.00 0.96 0.98 1.02 1.00 1.02 1.00

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Sleeper 1 Sleeper 2 Sleeper 3 Coastdown Constant Speed RSWT (WACD*A @ 7/55)***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 50 Next, the results from the RSWT were used to develop a virtual WAC d A value for coastdown testing . Specifically , the coastdown results and the WA C d A to C d A delta will be used to correct the coastdown results. As previously mentioned , we could not match the exact tractor model for RSWT and on - road testing for one of the tractors . In addition, we have not completed on - road testing for another tractor model that has been tested in the RSWT. Therefore, for this ex e rcise, we will use : the average of the RSWT results above for two out of the four sleeper cab tractors with trailer skirt s shown in the last row of Table 3 - 18 ; and th e average of coastdown results for two of the three tested sleeper cab tractor s with trailer skirts (average: 5.549 [n=2 ]) ; to demonstrate the coastdown yaw sweep correction . To begin the conversion from alternate method to coastdown, we first calculate certain parameters using the results from above: the wind average drag area

– zero yaw drag area offset; and the F

alt - aero using the coastdown and the zero yaw drag area results; shown in Table 3 - 19 below. **Table 3**  **- 19**  **Converting Wind Average Drag Area from the Alternate Method to Virtual Wind Average Drag**  **Area for the Coastdown Reference Method :**  **Sam ple Ca**  **lculations for Certified Configuration Calculations .**  CERTIFIED CONFIGURAT ION USING COASTDOWN REFERENCE METHOD AND ALTERNATE METHOD (SAMPLE DATA: RSWT RESULTS FOR DAY CAB IN TABLE 3 - 18 ) **Test Method/Source Variable**  **Value** Coastdown (reference method) ( C dA) zero,coastdown 5.5 Drag area from RSWT ( or other alt. method) ( C dA) zero,wind tunnel 4.9 Wind average drag area RSWT ( or other alt. method) ( C dA) wad wind tunnel 5.6 Alternate Method Factor F alt - aero F alt - aero = ( C dA) zero, coastdown / ( C dA) zero,wind tunnel = 5.5/4.9 = 1.12 Wind Average Offset WACd - CdA0 Offset ( C dA) wad,wind tunnel – ( C dA) zero,wind tunnel = 5.6

– 4.9 = 0.7 C dAwad Calculations ( for bin determination and GEM i nput) : Wind Average Equivalent Coastdown (C dA) wad ( C dA) wad = ( C dA) zero, coastdown + ( ( C dA) wad ,wind tunnel – ( C dA) zero,wind tunnel )* F alt aero = 5.5+(5.6 - 4.9)*1.12 = 5.5 + 0.7 *1.12 ( C dA) wad = **6. 3**  Using the Wind Average Equivalent Coastdown value of 6.2, a manufacturer would identify the appropriate bin for that value and use the associated aerodyn amic GEM input for determining CO 2 emissions and fuel consumption ; which is discussed below. For now, the alternate method factor, F alt - aero , is not used, however, it will be important later for certifying additional configurations. Once the certified configuration values have been derived , the alternate aerody namic method can be used to certify additional configurations using the F alt - aero from the certified configuration. For this example, we will use the same data from Table 3 - 18 and from Table 3 - 19 above for the Day

Cab to represent a completel y different configuration since the data from the sleeper cab tractors is all very similar (Note: In reality , a manufacturer would not be allowed to***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 51 use the day

cab for sleepe r certification, and vi ce versa). Thus, this approach is limited to the example calculations for illustrative purposes ) . Table 3 - 20 shows the calculations using the data from Table 3 - 18 and Table 3 - 19 for the day cab . Specificall y, Table 3 - 20 shows two cases: a case where the manufacturer has generated the wind average drag area from the alternate method and another case where the manufacturer does not have the wind average drag area but, instead, has the zero yaw drag area from the alternate method. In the latter case where the manufacturer does not have the wind average drag area, we are proposing that the manufacturer would use a default wind average drag area - zero yaw drag area of 0.80. **Table 3**  **- 20**  **Converting Wind Average Drag Area from the Alternate Method**  **to Virtual Wind Average Drag Area for the Coastdown Reference Method: Sam** **ple Calculations for Additional Configurations Using RSWT Day Cab Data**  ADDITIONAL CERTIFIED CONFIGURATIONS USING ALTERNATE METHOD (SAMPLE DATA: RSWT RESULTS FOR DAY CAB IN TABLE 3 - 18 ) Test Method/Source Variable Example: Previous Certified Configuration

Data Additional Configuration using Alternate Method ( Example: Day Cab Data) Coastdown (reference method) (C dA) zero,coastdown 5.5 Not Available ; alternate method used Alt. method Drag area ( C dA) zero, alt method 4.9 5.3 Alt. method wind average drag area ( C dA) wad ,alt method 5. 6 5.8 Calculated Using Certified Configuration in Table 3 - 19 Alternate Method Factor (F

alt - aero ) F alt - aero = ( C dA) zero,coastdown / ( C dA) zero,wind tunnel = 5.5/4.9 = 1.12 ( from Table 3 - 19 for certified case ) Actual Wind Average Offset WACd - CdA0 Offset 0.7 0.5 Default Wind Average Offset Default Offset 0.8 0.8 CdAwad Calculations (for bin determination and GEM input) : With ( C dA) wad , alt method ( C dA) wad = ( C dA) wad ,alt method * F alt aero = 5.6 * 1.12 = **6.3** ( C dA) wad = ( C dA) wad ,alt method * F alt - aero = 5.8 * 1.12 = **6.5** Without ( C dA) wad , alt method ; Instead, use ( C dA) zero, coastdown (if applicable) or ( C dA) zero, alt method with a default offset value of 0.80 ( C dA) wad = ( C dA) zero,coastdown +

default offset = 5.5 + 0.80 = **6.3** Not Applicable; Only alternate method is used ( C dA) wad = ( C dA) zero,alt method * F alt aero + default offset = 4.9 * 1.12 + 0.80 = **6.3** ( C dA) wad = ( C dA) zero, alt method * F alt - aero + default offset = 5.3 * 1.12 + 0.80 = **6.7** In contrast to F

alt - aero that is calculated once for the certified configuration and may be applied to additional configurations, the wind average drag area

– drag area ( WAC d A

– C d A ) offset is configuration dependent, and must be calculated for and used solely for that configuration. It may

be possible to use a single wind average – drag area offset for grouping***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 52 similar configurations but this would need to be supported b y d ata showing the level of variation between the configurations to justify such a grouping , and approved b y the agencies prior to use . Now that we have applied the adjustment for wind average drag area to the coastdown, we will revisit the method compariso n using this approach. Below in Figure 3 - 10 is the data from Figure 3 - 9 with the values for coastdown adjusted to account for wind average drag. In addition, the constant speed test results have been adjusted by the same factor to adjust for wind average and maintain its relative agreement with the coastdown test results. As shown in Figure 3 - 10 , the results for the RSWT are lower than the coastdown test results, as expected. Further, of note is the fact that if we anal yz e the method agreement for the zero yaw RSWT test results for a trailer with a skirt, prior to wind average adjustment and normalized to the coastdown test results, you would get results of 0.91 for Sleeper 1, 0.89 for Sleeper 2, and 0.90 for Sleeper 3. These are the results s hown in Figure 3 - 10 , demonstrating that the equations above are adequatel y accounting for wind average drag area in the coastdown results (e.g., the relative differenc e between the adjusted coastdown and RSWT wind average drag area is the same as the relative difference between the original coastdown result and the zero yaw drag area).***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 53 **Figure 3**  **- 9 Adjusted Method Comparison for Coastdown, Constant Speed and RSWT (WACdA @ 55 mph**  **w/ 7 m ph wind) Testing**  **Normalized to the Coastdown Results with wind average adjustment applied, for**  **Class 8 High Roof Sleeper Cab Tractors and Trailers Equipped with Trai ler Side Skirts**  **. Note: The results of**  **Sleeper 1 and Sleeper 3 are not directly com parable since the test articles do not m**  **atch but are shown to**

**represent overall industry trend given a m anufacturer’s unique fleet.**  1.00 1.00 1.00 0.96 0.98 1.02 0.91 0.89 0.90

0.00 0.20 0.40 0.60 0.80 1.00 1.20

Sleeper 1 Sleeper 2 Sleeper 3 Coastdown Constant Speed RSWT (Cd*A @ zero yaw)***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 54 Finally , below in Table 3 - 21 are the wind average equivalent coastdown values to illustrate how today ’s tractors fit into the proposed HD Phase 2 aerodynam ic standards. These values were developed using the coastdown results for each tractor and trailer equipped with a trailer side skirt , and applyingthe principles above with the corresponding zero yaw drag area and wind - average drag area from the RSWT. The corresponding aerodyn amic bins and GEM input are provided as well based on the proposed bin values in Section III.E.(2)(a)(iv) of the preamble . A manufacturer would use the resulting aerody namic GEM input to generate the configuration - specific CO 2 emission and fuel consumption value for certification. As shown below, most tractors today would qualify for Bin III with varying degrees of opportunity to move into improved bins. **Table 3**  **- 21**  **Wind Average Equivalent Coastdown Values Used to D evelop the**  **Proposed HD**  **Phase 2**

**Aerodynam ic Standards and Corresponding Aero Bin and Aero GEM Input.**  TRACTOR CONFIG CSTDWN C d A 0 WAC

d F

alt - aero WAC

d OFFSE T WAC

d X F alt - aero CSTDWN

+ WAC

d OFFSET HD PHASE

2 PROPOSED BIN # BIN III

AERO TEST RESULT BIN III

AERO GEM INPUT S leeper 1 skirt 5.4 4.91 5.42 1.11 0.505 **6.0 6.0**  Bin III 6.0 - 6.5 6.3 S leeper 2 skirt 5.6 4.96 5.70 1.15 0.742 **6.5 6.4**  Bin III 6.0 - 6.5 6.3 S leeper 3 skirt 5.6 5.06 5.60 1.11 0.542 **6.2 6.2**  Bin III 6.0 - 6.5 6.3 This table is only

intended to illustrate how the tractors would fit into the proposed bin structure but may

not be completely

appropriate for bin setting . Specifically , i n two cases, there were tractors where either the model designation or model year did not match between the on road and RSWT testing. As a result, it is better to look at the data in aggregate rather than on an individual vehicle basis. Using the average of the coastdown drag areas ( avg = 5.5), the average of the wind average offsets ( avg = 0.6), and the alternate method factor (Falt - aero) of 1.15 from the tractor (Sleeper 2) with matching vehicles between on - road and wind tunnel testing ; in the equation in Table 3 - 18 for a certified configuration (e.g., CdAzero, coastdown + (CdAwad , wind tunnel – CdAzero, wind tunnel ) * F alt aero ) you get a CdAwad value of 6.23. This value is almost exactly in the middle of the proposed Bin III standards and, therefore, we think that the proposed standards are appropriate. Further , the data in the Table 3 - 21 above provides some insight into the variability and range of high roof sleeper cab tractors from across the manufacturers that might be expected to be certified for HD Phase 2 . Thus, althou gh we do not have a complete set of matching datasets in all cases , we believe the values and bandwidth are appropriate for the HD Phase 2 proposed bin standards based on the data and calculations above . 

### 3.2.10 **Delta Drag Area Results to Support**  **Proposed HD**  **Phase 2 Trailer**  **Regulations** Similar to the tractor aerody namic assessment in Section 3.2.9 above, we can use the data generated during our aerody namic assessment test programs to support development of trailer aerodynamic standards. As previously discussed in Section 3.2.5 , the proposed trailer r egulations would use the delta C d A from an y of the accepted aerodyn amic methods. Table 3 - 22 below shows the delta C d A s across tractors, trailers , trailer configurations and aerody namic test***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 55 methods using data from Table 3 - 8 , Table 3 - 9 and Table 3 - 10 . The corresponding trailer certification bin and trailer aerodynamic GEM input s are provided as well based on the proposed values in Section IV of the preamble, IV. F.(3)(b)(iv), Table IV - 31. **Table 3**  **- 22**  **Delta C**  **D A**  **s from Various Tractors, Trailers, Trailer Configurations and Aerodynam ic Test**  **Me th**  **ods with Corresponding Trailer Aerodynam ic Bins**  CAB TYPE CONFIGURATION DELTA C **d** A (VS. STANDARD) TRAILER CERT. BI N TRAILER AERO

GEM I NPUT Coastdown Testing Sleeper 1 With Trailer Skirt #2 0.5 III 0.5

With Trailer Skirt and Boat Tail 0.9 IV 0.9 Sleeper 2 With Trailer Skirt #2 0.6 III 0.5

With Trailer Skirt and Boat Tail 1.1 IV 0.9 Sleeper 3 With Trailer Skirt #2 0.5 III 0.5

With Trailer Skirt and Boat Tail 0.7 IV 0.9 Constant Speed Testing Sleeper 1 With Trailer Skirt #2 0.7 IV 0.9

With Trailer Skirt and Boat Tail 1.1 IV 0.9 Sleeper 2 With Trailer Skirt #2 0.5 III 0.5 Reduced Scale Wind Tunnel Testing (RSWT) Sleeper 1 With Trailer Skirt #1 0.423 III 0.5 With Trailer Skirt #2 0.511 III 0.5 With Boat Tail 0.340 III 0.5 With Trailer Skirt #2 and Boat Tail 0.972 IV 0.9 Sleeper 2 With Trailer Skirt #1 0.586 III 0.5 With Trailer Skirt #2 0.594 III 0.5 With Boat Tail 0.365 III 0.5 With Trailer Skirt #2 and Boat Tail 1.092 IV 0.9 Sleeper 3 With Trailer Skirt #1 0.477 III 0.5 With Trailer Skirt #2 0.566 III 0.5 With Boat Tail 0.318 III 0.5 With Trailer Skirt #2 and Boat Tail 1.056 IV 0.9 Sleeper 4 With Trailer Skirt #1 0.481 III 0.5 With Trailer Skirt #2 0.557 III 0.5 With Boat Tail 0.332 III 0.5 With Trailer Skirt #2 and Boat Tail 1.121 IV 0.9 Day With Trailer Skirt #1 0.256 II 0.2

With Trailer Skirt #2 0.311 III 0.5 With Boat Tail 0.370 III 0.5 With Trailer Skirt #2 and Boat Tail 0.699 III 0.5 In general, Table 3 - 22 shows that individual components (e.g., trailer side skirts, boat tails) added to a trailer might qualify for Bin III while combinations of devices (e.g., trailer side skirt and boat tail) ad ded to a trailer might qualify for Bin IV. For the day

cab, a basic skirt such***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 56 as Skirt #1 would qualify for Bin II as opposed to an advance skirt such as Skirt #2 which would qualify for Bin III. Trailer manufacturers would follow a similar process of us ing the delta C d A values for their trailer devices or improved trailer designs to identify the appropriate trailer certification bin and the trailer aero GEM input for that bin. Accordingl y, these values were used to develop the trailer certification bins and aero GEM inputs to support the trailer regulations in HD Phase 2. 

### 3.3 **Tire Rolling Resistance** The agencies are proposing that the ISO 28580 test method be used to determine rolli ng resistance and the coefficient of rolling resistance. A cop y of the test method can be obtained through the American National Standards Institute. 13 

### 3.3.1 **Reason for Using ISO 28580** EPA’s SmartWay

Partnership Program started to identify equipment and feature requirements for SmartWay - designated Class 8 over - the - road tractors and trailers in 2006. In order to develop a tire rolling resistance specification for SmartWay - designated commercial trucks, EPA researched different test methods used to evaluate tire ro lling resistance, reviewing data and information from tire manufacturers, testing laboratories, the State of California, the Department of Transportation, tractor manufacturers, and various technical organizations. After assessing this information, EPA de termined that its SmartWay program would use the SAE J1269 14 tire rolling resistance method until the I SO 28580 15 method (at that time under development) was finalized, at which time the Agency would consider moving to this method fo r its SmartWay

program. D uring this same time period, the National Highway Traffic Safety

Administration (NHTSA) conducted an evaluation of passenger vehicle tire rolling resistance test methods and their variability . 16 Five different laboratory test methods at two separate labs w ere evaluated. The NHTSA study focused on passenger tires; however, three of the four test methods evaluated can be used for medium - duty and heav y- duty tractor tires. The methods evaluated were SAE J1269, SAE J2452 17 (not applicable for medium - duty or heavy- duty tractor tires), ISO 18164 18 and I SO 28580. The NHTSA study showed significant lab to lab variability between the labs used. The variability

was not consistent between tests or ty pes of tire within the same test. The study concluded that a method to account for this variability is necessary

if the rolling resistance value of tires is to be compared (NHTSA, 2009). Because of laboratory variability , NHTSA recommended that the use of ISO 28580 is preferred over the other test methods referenced. ISO 28580 is preferred because the test method involves laboratory alignment between a “reference laboratory” and “candidate laboratory .” The I SO technical committee involved in developing this test method also has the responsibility for determining the laboratory that will serve as the reference laboratory . The reference laboratory would make available an alignment tire that can be purchased by candidate laboratories. The candidate laboratory would identify

its reference machine. However, at this time, the reference laboratory and alignment tires have not been identified.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 57 

### 3.3.2 **Measurement Method and Results** The I SO 28580 test method includes a specific methodology for “light truck, commercial truck and bus” tires, and it has 4 measurement methods, force, torque, deceleration, and power, all of which appear to be suitable for use. The results of the ISO 28580 test are intended for use in vehicle simulation modeling, such as the model used to assess the effects of various technology options for national greenhouse gas and fuel econom y requirements for commercial trucks (see C hapter 4). The results are usually

expressed as a rolling resistance coefficient and measured as kilogram per metric ton (kg/metric ton) or as dimensionless units (1 kg/metric ton is the same a s the dimensionless unit 0.001). The results are corrected for ambient temperature drum surface and drum diameter as specified in the proposed test method. 

### 3.3.3 **Sample Size** The rolling resistance of tires within the same model and construction are expected to be relativel y uniform. In the study conducted b y NHTSA, only one individual tire had a rolling resistance value that was significantl y different from the other tires of the same model. The effect of production variability can be further reduced by conduc ting three replicate tests and using the average as the value for the rolling resistance coefficient. Tire models available in multiple diameters may

have different values of rolling resistance for each diameter because larger diameter tires can produce l ower rolling resistance than smaller diameters under the same load and inflation conditions . If the size range within a tire model becomes large enough that a given tire size is no longer “substantiall y similar” in rolling resistance performance to all other tire sizes of that model, then good engineering judgment should be exercised as to whether the differentl y- sized tire shall be treated, for testing and vehicle simulation purposes, as a distinct tire model. For Class 8 tractors that ty pically use tire s that fit on 22.5” or 24.5” wheels, this situation might occur with 17.5” tires, more commonl y used on moving vans and other applications that require a low floor. 

### 3.3.4 **Tire Size** In Phase 2, the agencies propose to require manufacturers to enter the tire loade d radius as a GEM input. While this rulemaking does not include tire size among the technologies applied to improve fuel efficiency , this measurement is among the driveline parameters necessary for GEM to calculate a vehicle speed for a given engine speed . Because there is a wide range of possible measurements for loaded radius, the agencies are specifying a proposed measurement procedure. Tire sizes can be measured using an overall diameter or a static loaded radius. Def

lection is ty

pically between 24 and 33 percent depending on the tire design. In the first 100 - 200 miles of a tire’s useful life, there will be a break - in process during which a commercial tire can “grow” one to two percent, up to 18 mm. Because this growth affects the air pressure in the tire, it’s important to specify the air pressure under which the loaded radius measurement is performed. The Society of Automotive Engineers (SAE) has published recommended practice J1025 for determining the revolutions per mile of new truck tires. 19 C onsistent with that recommended practice, the agencies propose that manufacturers would quantify the loaded tire radius of the drive tire, NIST traceable within ±0.5 percent uncertainty ,***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 58 by measuring the perpendicular distance from the axis of rotation of the loaded tire to the surface on which it is rolling. L oad the tire to 85 percent of the maximum load capacity specified by

the manufacturer, at the corresponding air inflation level. See 40 CFR 1037.520(j). 

### 3.4 **Duty Cycle**  Certification duty cycles have a significant impact on the GHG emissions from a truck and how technologies are assessed. Every truck has a different duty cycle in - use. Therefore, it is very challenging to develop a uniform duty cycle which accuratel y assesses GHG improveme nts and fuel efficiency from technologies relative to their performance in the real world. The duty cycle attributes that impact a vehicle’s performance include average speed, maximum speed, acceleration rates, deceleration rates, number of stops, road grade, power take off operation, and idling time. Average and maximum speeds are the attributes which have the greatest impact on aerodynamic technologies. Vehicle speed also impacts the effect of low rolling resistance tires. The effectiveness of extend ed idle reduction measures is determined b y the amount of time spent idling. Lastly , hy brid technologies demonstrate the greatest improvement on cycles which include a significant amount of stop - and - go driving due to the opportunities to recover braking energy . In addition, the amount of power take - off operation will impact the effectiveness of some vocational h ybrid applications. The ideal dut y cycle for a line - haul truck would account for a significant amount of time spent cruising at high speeds. A pi ckup and delivery truck duty c ycl e would contain a combination of urban driving, some number of stops, and limited highway driving. If the agencies propose an ill - suited duty cycle for a regulatory subcategory , it may

drive technologies where they

may not see the in - use benefits. For example, requiring all trucks to use a constant speed highway duty cycle would drive significant aerodynamic improvements. However, in the real world a pickup and delivery truck may

spend too little time on the highway to re alize the benefits of aerodynamic enhancements. In addition, the extra weight of the aerodyn amic fairings would actuall y penalize the GHG performance of that truck in urban driving and may reduce its freight carrying capability . 

### 3.4.1 **Duty Cycles Considered**  In HD Phase 1, the agencies selected three duty c ycles for certification testing: the Transient portion of the California Air Resource Board (CARB) Heav y Heavy- Dut y Truck 5 M ode Cycle, 55 mph cruise (without grade), and 65 mph cruise (without grade). For HD Phase 2, the agencies carefull y considered which duty cycles are appropriate for the different regulatory

subcategories. We considered several duty cycles in the development of the rulemaking including EPA’s MOVES model; the L ight - Duty FTP75 and HFET; Heavy- Dut y UDDS; World Wide Transient Vehicle C ycle (W TVC); Highway L ine Haul; Hy

brid Truck User Forum (HTUF) cycles; and California CARB’s Heavy - Heavy- Duty Truck 5 Mode Cycle. MOVES Medium - Duty

and Heavy - Duty

schedules were developed based on three studies. Eastern Research Group (ERG) instrumented 150 medium and heavy- duty vehicles, Battelle instrumented 120 vehicles instrumented with GPS, and Faucett instrumented 30 trucks***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 59 to characterize their in - use operation. 20 ERG then segregated the driving into freew ay and non freeway driving for medium and heav y- duty vehicles, and then further stratified vehicle trips according the predefined ranges of average speed covering the range of vehicle operation. Driving schedules were then developed for each speed bin b y creating combinations of idle - to idle “microtrips” until the representative target metrics were achieved. The schedules developed by ERG are not contiguous schedules which would be run on a chassis dy namometer, but are made up of non - contiguous “snippets” of driving meant to represent target distributions. This gives MOVES the versatility to handle smaller scale inventories, such as intersections or sections of interstate highway , independentl y. The FTP75 and HFET duty cycles are used extensively for L ight - Dut y emissions and CAFE programs. Our assessment is that these cycles are not appropriate for HD trucks for two primary reasons. First, the FTP has 24 accelerations during the cycle which are too steep for a Class 8 combination tractor to follow. S econd, the maximum speed is 60 mph during the HWFEC, while the national average truck highway speed is 65 mph. The Heav y- Dut y Urban Dynamometer Driving Cycle was developed to determine the Heav y- Duty

Engine FTP cycle. The cycle was developed from CAPE - 2 1 survey data which included information from 44 trucks and 3 buses in L os Angeles and 44 trucks and 4 buses in New York in 1977. The cycle was computer generated and weighted to represent New York non - freeway

(254 sec), Los Angeles non - freeway (285 sec), Los Angeles freeway (267 sec), New York non - freeway

(254 sec) to produce a nearly 50/50 weighting of highway cruise and urban transient. We believe this cycle is not appropriate for our program for several reasons. The maximum speed on the UDDS is 58 mp h which is low relative to the truck speed limits in effect today . The 50/50 weighting of cruise to transient is too low for combination tractors and too high for vocational vehicles and the single cycle does not provide flexibility to change the weightin gs. Lastl y, the acceleration rates are low for today’s higher power trucks. The World Harmonized WTVC was developed by the UN ECE GRPE group. It represents urban, rural, and motorway operation. The cycle was developed based on data from 20 straight truc ks, 18 combination tractors, and 11 buses total from Australia, Europe, Japan, and the US. EPA has a desire to harmonize internationally , however, we believe that this single cycle does not optimally

cover the different ty

pes of truck operation in the Uni ted States and does not provide the flexibility to vary the weightings of a single cycle. The Highway

L ine Haul schedule was created by Southwest Research Institute, using input from a group of stakeholders, including EPA, Northeastern States for Coordinat ed Air Use Management (NESCAUM), several truck and engine manufacturers, state organizations, and others, for a NESCAUM heav y truck fuel efficiency modeling and simulation project. The cycle is 103 miles long and incorporates grade and altitude. This cyc le is a good representation of line haul operation. However, the altitude changes cannot be incorporated into a chassis dy namometer or track test and the cycle is also too long for a typical chassis dynamometer test. The Calstart - Weststart Hy brid Truck Users Forum is developing cycles to match the characteristics of truck applications which are expected to be first to market for hy brids. The cycles include the Manhattan Bus Cycle, Orange County Bus C ycle, Class 4 Parcel Delivery, Class 6 Parcel Delivery , Combined International Local and Commuter C ycle (CILCC),***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 60 Neighborhood Refuse, Utility Service, and Intermodal Drayage cycles. The cycles are very application - specific and appropriatel y evaluate each vocation. However, the use of these ty pes of applicat ion specific cycles in a regulatory scheme would lead to a proliferation of cycles for every application, an outcome that is not desirable. The CARB 5 Mode cycle was developed by California CARB from heav y- duty truck data gathered from 1997 through 2000. 21 Data was collected from real world driving from randomly selected vehicles. The data was gathered from 140 heavy- duty trucks by Battelle and from 31 heav y- duty

trucks in a study

conducted by

Jack Faucett and Associates. The final data set included 84 of these heav y duty trucks covering over 60,000 miles and 1,600 hours of activity . The cycles were developed to reflect ty pical in - use behavior as demonstrated from the data collected. The four modes (idle, creep, transient, and cruise) were determined as distinct operating patterns, which then led to the four drive schedules. The cycle is well accepted in the heav y- duty industry . It was used in the CRC E55/59 Study which is the largest HD chassis dy namometer study

to date and used in MOVES and EMFAC to d etermine emission rate inputs; EPA’s biodiesel study

which used engine dynamometer schedules created from CARB cruise cycle; the HEI ACES Study : WVU developed engine cycles from CARB 4 - mode chassis cycles; CE/CERT test; and by

WVU to predict fuel efficienc y performance on an y duty cycle from CARB 5 mode results. The modal approach to the cycles provides flexibility in cycle weightings to accommodate a variety of truck applications. A downside of the cycle is that it was developed from truck activity

in Ca lifornia only . 

### 3.4.2 **Proposed Duty**  **Cycles 3.4.2.1**  **Highw ay Cruise Cycles**  The agencies analyzed the average truck speed limit on interstates and other freeway s to identify the appropriate speed of the highway cruise cycles. State speed limits for trucks vary between 55 and 75 mph, depending on the state. 22 The median urban and rural interstate speed limit of all states is 65 mph. The agencies also analyzed the speed limits in terms of VMT weighting. The agencies used the Federal Highway Administration data on Annual Veh icle Miles for 2008 published in November 2009 to establish the vehicle miles travelled on rural and urban interstates broken down by state. The VMT - weighted national average speed limit is 63 mph based on the information provided in Table 3 - 23 . The results of this analy sis led to the adoption of the H igh S peed (65 mph) and L ow S peed (55 mph) C ruise duty cycle s in Phase 1 .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 61 **Table 3**  **- 23**  **VM T**  **- Weighted National Truck Speed Limit**  STATE RURAL

INTERSTATE SPEED LIMIT URBAN

INTERSTATE SPEED LIMIT RURAL

INTERSTATE MILES URBAN

INTERSTATE AND OTHER FREEWAYS MILES U.S.

WEIGHTED VMT FRACTION RURAL U.S.

WEIGHTED VMT FR AC TION URBAN VMT

WEIGHTED SPEED LIMIT AL 70 65 5,643 7,950 0.6% 0.8% 0.968 AK 55 55 803 662 0.1% 0.1% 0.086 AZ 75 65 6,966 13,324 0.7% 1.4% 1.474 AR 65 55 4,510 4,794 0.5% 0.5% 0.591 CA 55 55 17,681 123,482 1.9% 13.1% 8.242 CO 75 65 4,409 11,745 0.5% 1.2% 1.161 CN 65 55 715 13,485 0.1% 1.4% 0.837 DE 55 55 - 1,694 0.0% 0.2% 0.099 DC 55 55 - 813 0.0% 0.1% 0.047 FL 70 65 9,591 37,185 1.0% 3.9% 3.279 GA 70 55 9,433 21,522 1.0% 2.3% 1.958 HA 60 60 110 2,403 0.0% 0.3% 0.160 ID 65 65 2,101 1,250 0.2% 0.1% 0.231 IL 65 55 8,972 23,584 1.0% 2.5% 1.996 IN 65 55 7,140 10,850 0.8% 1.2% 1.126 IA 70 55 4,628 2,538 0.5% 0.3% 0.492 KA 75 75 3,242 5,480 0.3% 0.6% 0.694 KE 65 65 6,566 6,834 0.7% 0.7% 0.925 LA 70 70 5,489 7,708 0.6% 0.8% 0.981 ME 65 65 2,207 958 0.2% 0.1% 0.218 MA 65 65 3,484 18,792 0.4% 2.0% 1.537 MS 70 70 1,257 20,579 0.1% 2.2% 1.623 MI 60 60 5,245 20,931 0.6% 2.2% 1.667 MN 70 60 4,150 12,071 0.4% 1.3% 1.077 MS 70 70 4,103 4,004 0.4% 0.4% 0.602 MO 70 60 5,972 16,957 0.6% 1.8% 1.524 MT 65 65 2,350 343 0.2% 0.0% 0.186 NE 75 65 2,590 1,653 0.3% 0.2% 0.320 NV 75 65 1,826 5,286 0.2% 0.6% 0.510 NH 65 65 1,235 2,574 0.1% 0.3% 0.263 NJ 65 55 1,609 25,330 0.2% 2.7% 1.590 NM 75 65 4,530 2,667 0.5% 0.3% 0.545 NY 65 55 6,176 37,306 0.7% 4.0% 2.604 NC 70 70 5,957 19,216 0.6% 2.0% 1.871 ND 75 75 1,394 374 0.1% 0.0% 0.141***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 62 OH 65 65 9,039 27,830 1.0% 3.0% 2.544 OK 75 70 5,029 7,223 0.5% 0.8% 0.937 OR 55 55 4,109 5,734 0.4% 0.6% 0.575 PA 65 55 10,864 21,756 1.2% 2.3% 2.020 RI 65 55 404 2,948 0.0% 0.3% 0.200 SC 70 70 7,355 6,879 0.8% 0.7% 1.058 SD 75 75 1,960 648 0.2% 0.1% 0.208 TN 70 70 8,686 13,414 0.9% 1.4% 1.642 TX 70 70 15,397 71,820 1.6% 7.6% 6.481 UT 75 65 3,117 6,165 0.3% 0.7% 0.674 VT 65 55 1,216 443 0.1% 0.0% 0.110 VA 70 70 8,764 18,907 0.9% 2.0% 2.056 WA 60 60 4,392 15,816 0.5% 1.7% 1.287 WV 70 65 3,195 3,175 0.3% 0.3% 0.456 WI 65 65 5,197 9,139 0.6% 1.0% 0.989 WY 75 75 2,482 474 0.3% 0.1% 0.235 In establishing the highway cruise cycle s in Phase 1, we realize d that we did not address the effect of road grad e on emissions. Therefore, for Phase 2, we are proposing to alter the High Speed Cruise and Low Speed Cruise modes to reflect road grade for the constant speed cycles at 65 mph and 55 mph respectivel y. Based on input from trucking fleets and truck manufacturers, we believe this is representative of in - use operation, wherein truck drivers use cruise control whenever possible during periods of sustained higher speed driving and road grade varies. T o this e nd, the U.S. Department of Energy and EPA have partnered to support a project aimed at evaluating, refining and/or developing the appropriate road grade profiles for the duty cycles that would be used in the certification of heavy- duty vehicles to the GHG emission and fuel efficiency Phase 2 standards. The National Renewable Energy L aboratory

(NREL) is leading a project which will refine the existing highway cruise duty cycles. Inthe course of this work, NREL has developed several activity- weighted road grade profile s which are representative of U.S. limited - access highway s using high - accuracy road grade and count yspecific data for vehicle miles traveled. Either a single road grade profile representative of the nation’s limited - access highway s will be c hosen for use in the highway cruise cycles or two activity- weighted grade profiles will be selected if anal ys is demonstrates that they should be different for speed limits of 55 and 65 mph. The profiles are distance - based and cover a maximum distance of 1 5 miles . Inaddition to NRELwork, the agencies have independentl y developed another candidate road grade profile for use in the 55 mph and 65 mph highway cruise cycles. While based on the same road grade database generated by NRELfor U. S. restricted ac cess highway s, its design is predicated on a different approach. This analy sis of road grade profile options was not completed in time for use in developing the primary proposal . Therefore, f or the proposal, the agencies selected an interim road grade profile for development of the proposed standards , which is described in Section III.E of the preamble to these rules . Based on preliminary

results, it appears the interim road grade profile closel y matches a national road grade profile on an absolute basis , before VMT weighting. The report documenting th e NREL ’s***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 63 and the agencies’ road grade work is available to the publ ic in the docket, as is the agencies’ anal ys is of possible alternative vehicle standards developed using alternative road grade profiles. 

### 3.4.2.2 **Transient Cycle** T he Phase 1 rule requires use of the Transient portion of the CARB ’s Heavy Heavy- Duty Truck 5 Mode C ycle. The agencies have found that this cycle reasonabl y represents transient operation of man y heav y - duty vehicles, though it is a very sh ort test cycle - less than 3 miles

– and can be driven in roughly 11 minutes. We are not proposing an y changes to that cycle, and would continue to use it when certifying vehicles to the HD Phase 2 standards. The agencies would like to note that we have also launched a project at the National Renewable Energy

L aboratory

(NREL) to determine the extent to which the Transient mode of the CARB Heav y - Dut y Truck 5 Mode C ycle is representative of transient operation of Class 2b 8 vocational vehicles. This analy sis is being performed using NREL’s extensive vehicle activity database and a variety of metrics such as average driving speed, kinetic intensity , idle time, maximum driving speed and standard deviation of speed. Should NRELrecommend, and the agenc ies agree, that an y s ubcategory of vocational vehicles is poorly represented by

the Transient mode of the CARB cycle, a more representative transient test cycle will be adopted , p ossibly selected from test cycles already in use. T his analy sis was not comp leted in time for use in developing the primary proposal . The report documenting this work is available to the publ ic in the docket , as is the agencies’ anal ys is of possible alternative vocational vehic le standards developed using an alternative transient duty c ycl e . 

### 3.4.2.3 **Idle Cycle** We are also proposing the addition of an idle - onl y cycle to determine both fuel consumption and CO 2 emissions when a vehicle is idling, and recognize technologies that either reduce the fuel consumption rate or shut the engine off (and restart) during short - term idle events during the workday . The agencies are not expecting that this cycle would recogn ize technologies that allow the main engine to remain off during stationary vehicle operation with a PTO engaged and performing work. Those technologies would be recognized over the Hy brid - PTO test procedure defined in 40 CFR 1037.525. In this proposed i dle - onl y c ycl e, based on user inputs, GEM would calculate CO 2 emissions and fuel consumption at both zero torque (neutral idle) and with torque set to Curb - Idle Transmission Torque (as defined in 40 CFR 1065.510(f)(4) for variable speed engines) for use in the CO 2 emission calculation in 40 CFR 1037.510(b). We are also proposing that GEM would calculate reduced CO 2 and fueling for stop - start sy stems, based on an assumption that the effectiveness would represent a 90 percent reduction of the emissions that would occur if the vehicle had operated at Curb - Idle Transmission Torque over this cycle. This cycle is proposed to be applicable onl y for vocational vehicles using either the Regional, Multi - Purpose, or Urban composite duty cycles. 

### 3.4.3 **Weightings of Each Cyc le per Regulatory Subcategory**  Table 3 - 24 presents the Phase 1 final GEM duty cycle composite weightings for vocational vehicles and tractors.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 64 **Table 3**  **- 24**  **Phase 1 Vehicle**  **Duty Cycle**  **Com posite**  **Weighting s**  VEHICLE CATEGORY PHASE 1 COMPOSI TE WE IG HT INGS OF DUTY CYCLE MODE Transient 55 mph Cruise 65 mph Cruise Vocational 42% 21% 37% Vocational Hy

brid Vehicles 75% 9% 16% Day Cabs 19% 17% 64% Sleeper Cabs 5% 9% 86% 

### 3.4.3.1 **Vocational Vehicles** In order to properl y weight the “idle” time of each vehicle class and category independentl y of the idle time in the duty cycles, EPA is proposing that idle emissions are weighted with the driving cycles. In the HD Phase 1 rule the duty c ycl es were weighted b y distance to properl y reflect the vehicle miles traveled by each category . To incorporate “idle” emissions, the equ ation had to be modified to allow for the “idle” emissions to be time weighted with the driving cycles. The result of this is that the weighting factors for the driving cycles will still add up to 100 percent while the idle weighting factor will be less than 100 percent , reflecting the actual idle time of the vehicles b y category. The agencies are proposing to modify the equation in 40 CFR 1037.510(b) to accommodate both the distance (non - idle) and time based (idle) weighting factors. The proposed duty cycle weightings for each vocational vehicle test cycle are included in Table 3 - 25 . **Table 3**  **- 25**  **Proposed Phase 2**  **Duty Cycle Mode**  **Com posite**  **Weightings** VEHICLE CATEGORY DUTY CYCLE MODE

Transient 55 mph Cruise 65 mph Cruise Idle Vocational Regional 50% 28% 22% 10% Vocational Multi Purpose 82% 15% 3% 15% Vocational Urban 94% 6% 0% 20% 

### 3.5 **Tare Weights and Payload** We propose to continue defining the total weight of a truck as the combination of the truck’s tare weight, a trailer’s tare weight (if applicable), and the payload; as it was defined in the HD Phase 1 rule. The total weight of a truck is important because it in part determines the impact of technologies, such as rolling resistance, on GHG emissions and fuel consumption. As***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 65 the HD program is designed, it is important that the agencies define weights which are representative of the fleet while recognizing that the final weights are not representative of a specific vehicle. The sections below describe the agencies’ approach to defining each of these weights. 

### 3.5.1 **Truck Tare Weights** The tare weight of a truck will vary depending on many

factors, including the choi ces made b y the manufacturer in designing the truck (such as the use of lightweight materials, the cab configuration (such as day or sleeper cab), whether it has aerody namic fairing (such as a roof fairing), and the specific options on the truck. The Cla ss 8 combination tractor tare weights were developed based on the weights of actual tractors tested in EPA’s coastdown program. The empty weight of the Class 8 sleeper cabs with a high roof tested ranged between 19,000 and 20,260 pounds. The empty weight of the Class 8 day

cab with a high roof tested was 17,840 pounds. The agencies derived the tare weight of the Class 7 day

cabs based on the guidance of truck manufacturers. The agencies then assumed that a roof fairing weighs approximately 500 pounds. B ased on this, the agencies are proposing the tractor tare weights as shown i n Table 3 - 26 . **Table 3**  **- 26**  **Tractor Tare Weights** MODEL TYPE CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 7 CLASS 7 Regulatory Subcategory Sleeper

Cab High Roof Sleeper

Cab Mid Roof Sleeper

Cab L ow Roof Day

Cab High Roof Day

Cab Low Roof Day

Cab High Roof Day

Cab Low Roof Tractor Tare Weight (lbs) 19,000 18,750 18,500 17,500 17,000 11,500 11,000 The agencies developed the empty tare weights of the vocational vehicles based on the EDF report 23 on GHG management for Medium - Duty Fleets. The EDF report found that the average tare wei ght of a Class 4 truck is 10,343 pounds, of a Class 6 truck is 13,942 pounds, and a Class 8 truck is 23,525 pounds. The agencies are proposing to continue to use the following tare weights:  Li ght Heav y (Class 2b - 5) = 10,300 pounds  Medium Heav y (Class 6 - 7) = 13,950 pounds  Heav y Heav y (Class 8) = 23,500 pounds 

### 3.5.2 **Trailer Tare Weights** We propose to continue to define the trailer tare weights used in the tractor program based on measurements conducted during EPA’s coastdown testing and information gathered b y IC F in the cost report to EPA, as adopted in the HD Phase 1 rule. 24***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 66 A ty pical 53 foot box (or van) trailer has an empty weight ranging between 13,500 and 14,000 po unds per ICF’s findings. The box trailer tested by EPA in the coastdown testing weighed 13,660 pounds. Therefore, the agencies are defining the empty box trailer weight as 13,500 pounds. A ty pical flatbed trailer weighs between 9,760 and 10,760 per the s urvey conducted by IC F. EPA’s coastdown work utilized a flatbed trailer which weighed 10,480 pounds. Based on this, the agencies are defining a flatbed trailer weight of 10,500 pounds. Lastl y, a tanker trailer weight typicall y ranges between 9,010 and 10 ,500 pounds based on I CF findings. The tanker trailer used in the coastdown testing weighed 9,840 pounds. The agencies are defining the empty tanker trailer weight of 10,000 pounds. 

### 3.5.3 **Payload** The amount of payload by weight that a tractor can carry depends on the class (or GVWR) of the vehicle. For example, a typical Class 7 tractor can carry fewer tons of payload than a Class 8 tractor. Payload impacts both the overall test weight of the truck and is used to assess the “per ton - mile” fuel consumption and GHG emissions. The “tons” represent the payload measured in tons. M.J. Bradley

anal yz ed the Truck Inventory and Use Survey

and found that approximately 9 percent of combination tractor miles travelled empty , 61 percent are “cubed - out” (the trailer is f ull before the weight limit is reached), and 30 percent are “weighed out” (operating weight equal 80,000 pounds which is the gross vehicle weight limit on the Federal Interstate Highway Sy stem or greater than 80,000 pounds for vehicles traveling on roads o utside of the interstate sy stem). 25 The Federal Highway Administration developed Truck Payload Equivalent Factors to inform the development of highway s ys tem strategies using Vehicle Inventory and Use Survey (VIUS) and Vehicle Travel Information Sy stem (VT RI S) data. Their results, as shown in Table 3 - 27 , f ound that the average payload of a Class 8 truck ranged from 29,628 to 40,243 pounds, depending on the average distance travelled per day . 26 The same results found that Class 7 trucks carried between 18,674 and 34,210 pounds of payload also depending on aver age distance travelled per day . **Table 3**  **- 27**  **Nation al Average Payload (lbs.) per Distance Travelled and Gross Vehicle Weight Group**  **(VIUS) 27**  CLASS 3 CLASS 4 CLASS 5 CLASS 6 CLASS 7 CLASS 8 < 50 miles 3,706 4,550 8,023 10,310 18,674 29,628 51 to100 miles 3,585 4,913 6,436 10,628 23,270 36,247 101 to 200 miles 4,189 6,628 8,491 12,747 30,180 39,743 201 to 500 miles 4,273 7,029 6,360 10,301 25,379 40,243 > 500 mile 3,216 8,052 6,545 12,031 34,210 40,089 Average 3,794 6,234 7,171 11,203 26,343 37,190 The agencies are prescribing a fixed payload of 25,000 pounds for Class 7 tractors and 38,000 pounds for Class 8 tractors for their respective test procedures. These payload values***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 67 represent a heavily

loaded trailer, but not maximum GVWR, since as describe d above the majority of tractors "cube - out" rather than "weigh - out.” NHTSA and EPA are also proposing to continue using the payload requirements for each regulatory

subcategory

in the vocational vehicle category that were finalized in the HD Phase 1 rule . The payloads were developed from Federal Highway statistics based on the averaging the payloads for the weight classes of represented within each vehicle category. 28 The payload requirement is 5,700 pounds for the Light Heav y trucks based on the average payload of Class 3, 4, and 5 trucks from Table 3 - 27 . The payload for Medium Heavy trucks is 11,200 pounds per the average payload of Class 6 trucks as shown in Table 3 - 27 . Lastl y the agencies are defining 38,000 pounds payload for the Heavy Heavy trucks based on the average Class 8 payload in Table 3 - 27 . 

### 3.5.4 **Total Weight** In summary , the total weights of the combination tractors are shown in Ta ble 3 - 28 . **Ta ble**  **3 -**  **28 Combination Tractor Total Weight**  MODEL TYPE CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 7 CLASS 7 CLASS 7 Regulatory Subcategory Sleeper

Cab High Roof Sleeper

Cab Mid Roof Sleeper

Cab Low Roof Day Cab

High Roof Day Cab

Mid Roof Day Cab

Low Roof Day Cab

High Roof Day Cab

Mid Roof Day Cab

Low Roof Tractor Tare Weight (lbs) 19,000 18,750 18,500 17,500 17,100 17,000 11,500 11,100 11,000 Trailer Weight (lbs) 13,500 10,000 10,500 13,500 10,000 10,500 13,500 10,000 10,500 Payload (lbs) 38,000 38,000 38,000 38,000 38,000 38,000 25,000 25,000 25,000 Total Weight (lbs) 70,500 66,750 67,000 69,000 65,100 65,500 50,000 46,100 46,500 The total weights of the vocational vehicles are as shown in Table 3 - 29 . **Table 3**  **- 29**  **Vocational Vehicle Total Weights** REGULATORY SUBCATEGORY LIGHT

HEAVY MEDIUM

HEAVY HEAVY

HEAVY Truck Tare Weight (lbs) 10,300 13,950 27,000 Payload (lbs) 5,700 11,200 15,000 Total Weight (lbs) 16,000 25,150 42,000 

### 3.6 **Powertrain Test Procedures** In the HD Phase 1 rule the agencies introduced a powertrain test procedure to allow manufacturers to generate credits for selling advanced powertrains that reduced CO 2 emissions and fuel consumption. In Phase 2 we are proposing to bring the powertrain test procedure into the main program and project that 15 to 30 percent of the vocational vehicles (including both hy brid and non - hy

brid applications) would certify using this method. To accommodate this***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 68 change we are proposing a number of improvements to the test pro cedure in 40 CFR 1037.550 and reducing the test burden by onl y requiring testing of the powertrain that is to be certified. The agencies are also proposing m odifications to 40 CFR 1037.550 to separate out the h ybrid specific testing protocols. 

### 3.6.1 **Reason Behi**  **nd Use Of Powertrain Test Method f**  **or Conventional a**  **nd Hybrid Powertrain Certification**  The agencies are proposing a powertrain test option to afford a robust mechanism to quantify the benefits of CO 2 reducing technologies that are a part of the powertrain (conventional or hy brid), that are not captured in the GEM simulation. Among these technologies are transient fuel control, engine and transmission control integration, and hy brid s ys tems. The larg est proposed change from the Phase 1 powertrain procedure is that onl y the advanced powertrain will need to be tested as opposed to the requirement in Phase 1 where the result was an improvement factor calculated from the powertrain results of both the adv anced powertrain and the conventional powertrain. This proposed change is possible because the proposed GEM simulation tool uses the engine fuel map and torque curve from the actual engine in the vehicle that is to be certified for all vehicles that do no t use the powertrain method to certify the vehicle . 

### 3.6.2 **Use of Generic Vehicles t**  **o Apply Measurements Broadly Across All Vehicles That the Powertrain Will Be Installed In**  To limit the amount of testing, under the proposal, powertrains will be divided into fami lies and will be tested in a limited number of simulated vehicles that will cover the range of vehicles in which the powertrain will be used. A matrix of 8 to 9 tests w ould be needed per vehicle cycle, to enable the use of the powertrain results broadly ac ross all the vehicles in which the powertrain will be installed. The individual tests differ by

the vehicle that is being simulated during the test. Table 3 - 30 and Table 3 - 31 define the unique vehicles being proposed that w ould cover the range of coefficient of drag, coefficient of rolling resistance, vehicle mass and axle ratio o f the vehicles that the powertrain will be installed in. To allow for a generic tire size definition that will cover the tires and axles installed on the certified vehicles, the agencies are proposing that each tire radius will be set so that when the vehi cle is cruising at 65 mph the engine speed will equal the corresponding minimum NTE exclusion speed as defined in 40 CFR part 86.1370(b)(1), intermediate test speed (A, B, or C) , or maximum test speed defined in 40 CFR part 1065. To calculate the tire radius , use the equation in 40 CFR 1037.550.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 69 **Table 3**  **- 30**  **Proposed Generic Vehicle Definitions for Class 2b -**  **7 Vehicles** TEST 1 TEST 2 TEST 3 TEST 4 TEST 5 TEST 6 TEST 7 TEST 8 Mass (kg) 7,257 11,408 7,257 11,408 7,257 11,408 7,257 11,408 C d A 5.4 5.4 5.4 5.4 5.4 5.4 5.4 5.4 Tire C rr (kg/ton) 6.7 6.9 6.7 6.9 6.7 6.9 6.7 6.9 Tire Radius (m) 0.426 0.426 0.426 0.426 0.426 0.426 0.426 0.426 Rotating Inertia (kg) 454 454 454 454 454 454 454 454 Axle Gear Efficiency (%) 95.5 95.5 95.5 95.5 95.5 95.5 95.5 95.5 Accessory Power (W) 1300 1300 1300 1300 1300 1300 1300 1300 Axle ratio at engine speed A A B B C C Maximum engine speed Maximum

engine speed

**Table 3**  **- 31**  **Proposed Generic Vehicle Definitions for Tractors**  **and Class 8**  **Vocational Vehicles —**  **General Purpose**  TEST 1 TEST 2 TEST 3 TEST 4 TEST 5 TEST 6 TEST 7 TEST 8 TEST 9 Mass (kg) 31,978 22,679 19,051 31,978 22,679 19,051 31,978 22,679 19,051 C d A 5.4 4.7 4.0 5.4 4.7 4.0 5.4 4.7 4.0 Tire C rr (kg/ton) 6.9 6.9 6.9 6.9 6.9 6.9 6.9 6.9 6.9 Tire Radius (m) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Rotating Inertia (kg) 1,134 907 680 1,134 907 680 1,134 907 680 Axle Gear Efficiency (%) 95.5 95.5 95.5 95.5 95.5 95.5 95.5 95.5 95.5 Accessory Power (W) 1300 1300 1300 1300 1300 1300 1300 1300 1300 Axle ratio at engine speed Minimum

NTE exclusion speed Minimum

NTE exclusion speed Minimum

NTE exclusion speed B B B Maximum engine speed Maximum

engine speed Maximum

engine speed***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 70 **Table 3**  **- 32**  **Proposed Generic Vehicle**  **Definitions for Class 8 Combination —**  **Heavy -**  **Haul Vehicle** TEST 1 TEST 2 TEST 3 TEST 4 TEST 5 TEST 6 TEST 7 TEST 8 TEST 9 Mass (kg) 40,895 31,978 22,679 40,895 31,978 22,679 40,895 31,978 22,679 C d A 6.1 5.4 4.7 6.1 5.4 4.7 6.1 5.4 4.7 Tire C rr (kg/ton) 6.9 6.9 6.9 6.9 6.9 6.9 6.9 6.9 6.9 Tire Radius (m) 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Rotating Inertia (kg) 1,134 907 680 1,134 907 680 1,134 907 680 Axle Gear Efficiency (%) 95.5 95.5 95.5 95.5 95.5 95.5 95.5 95.5 95.5 Accessory Power (W) 1300 1300 1300 1300 1300 1300 1300 1300 1300 Axle ratio at engine speed Minimum

NTE exclusion speed Minimum

NTE exclusion speed Minimum

NTE exclusion speed B B B Maximum engine speed Maximum

engine speed Maximum

engine speed The main output s of this matrix of tests is grams of CO 2 , the average transmission output shaft speed divided b y the average vehicle speed and positive work measured at the output shaft of the powertrain. This matrix of test results will then be used to calculate the vehicle ’ s CO 2 emissions in GEM taking the work per ton - mile from the GEM simulation and multiplying it by the interpolated work specific CO 2 mass emissions from the powertrain tes t. 

### 3.6.3 **Measurement Method and Results** The agencies are proposing to expand upon the test procedures defined 40 CFR 1037.550 for HD Phase 1. The Phase 2 proposed expansion will migrate the current Phase 1 test procedure to a new 40 CFR 1037.555 and will modify the current test procedure in 40 CFR 1037.550, allowing its use for Phase 2 only . The Phase 2 modifications to 40 CFR 1037.550 include the addition of the rotating inertia of the driveline and tires, the axle efficiency and the vehicle’s accessory loads. This revised procedure also requires that each of the powertrain components be cooled so that the temperature of each of the components is kept in the normal operation range. In addition to changing the vehicle model, we are proposing changes to the dri ve model so that it can compensate when the powertrain gets ahead or falls behind in the duty cycle. Use of this compensation algorithm will ensure that every powertrain drives the complete distance of the cycle, regardless of whether or not it can maintain the target speed of the cycle at a given moment in time. Although detailed equations for the vehicle and driver models can be found in the proposed 40 CFR 1037.550, the agencies are recommending that manufactures use the MATLAB and Simulink models prov ided by the agencies. These models can be found at http://www.epa.gov/otaq/climate/gem.htm .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 71 Conventional Powertrain T est Results The agencies have performed internal test programs, contracted with outside labs, as well as collaborated with manufactures to test out the improvements to the powertrain test procedure. T he data presented in Figure 3 - 10 is from a conventional powertrain that consisted of a Cummins ISX engine and Eaton 10 speed automated manual transmission that was tested in one of these test programs . This data summarizes the results from three different types of tests. The first set of data , labeled “E ngine O nly” , was collected from engine tests where the speed and torque setpoints were determined by GEM. The simulations were done with 9 different vehicle configurations over the three duty cycles that are being proposed as certification duty cycles (55 mph with grade, 65 mph with grade and ARB transient cycle). The “GEM Model” data contains the CO 2 emissions as determined b y GEM using the engine ’ s fuel map and the trans mission ’ s gear ratios using with the default shift strategy . The x - axis defines the P owertrain test results . The data shows that a cross all three test cycles the powertrain test procedure produces 2.5 percent less CO 2 emission than the GEM simulation predicted . One must, however, take into account the fact that the GEM simulation was done using the engine steady- state fuel map ; thus , the GEM results don’t fully take into account the effect of transient fueling on CO 2 emissions . This is evident when l ooking at the data collected when operating over the transient test cycles (highest CO 2 g/ton - mile results) . Here you see that the engine consumed greater than 3 percent more fuel than GEM predicted. When taking the transient test results into account , the powertrain performed 5 to 8 percent better than GEM predicted.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 72 **Figure 3**  **- 10**  **Engine only and GEM CO 2**  **results vs. powertrain.******* E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 73 

### 3.6.4 **Powertrain Family Definition** To complement the agencies powertrain procedures we are proposing criteria for defining a powertrain famil y. The specifics of these criteria can be found in 40 CFR 1037.23 1 but nominally

a powertrain family

is made up of one engine famil y and one transmis sion family . 

### 3.6.4.1 **Criteria for Powertrain**  **Families** The proposed regulations in 40 CFR 1037.231 outline the criteria for grouping transmission models into powertrain families sharing similar emission characteristics. A few of these defining criteria include the transmission ’ s architecture (manual, automatic, automated manual, dual - clutch and hy brid) , number of gears in the front box, number of meshes in the back box and dry

sump versus regular sump . In addition to the criteria for the transmission , all the engi nes in the powertrain family have to be from the same engine famil y. 

### 3.6.4.2 **Emissions Test Powertrain**  We are proposing that manufacturers select at least one powertrain per powertrain family for emission testing. The methodology for selecting the test powertrain (s) should be consistent with 40 CFR 1037.231 . The test powertrain(s) should consist of the engine and transmission combination that results in the highest CO 2 emissions . 

### 3.6.5 **Vehicle Certification with Powertrain Results in GEM** For manufactures that choose to use the powertrain method when certifying a vehicle, the powertrain results from the test will be input into GEM instead of the engine’s fuel map, torque curve, motoring curve and the transmissions gear ratios. GEM will use the default powertrain inputs , as described in Table 3 - 33 , and the inputs of the to - be certified vehicle to calculate the cycle work ( W

) of the powertrain and the ratio of rotational speed over the vehicle speed ( N / V ) as defined b y the tire radius and rear - axle ratio .

**Table 3**  **- 33**  **GEM Default Param**  **eters for Vehicle Certification Using Powertrain Testing.** REGULATORY CLASS ENGINE TRANSMISSION GEAR RATIOS Class 8 Com bination Heavy - Haul 2017 MY 15L Engine with 600 HP 13 speed

Automated Manual Transmission 12.29, 8.51,

6.05, 4.38, 3.20, 2.29, 1.95, 1.62, 1.38, 1.17, 1.00, 0.86, 0.73 Sleeper Cab - High Roof 2017 MY 15L Engine with 455 HP 10 speed

Automated Manual Transmission 12.8, 9.25, 6.76,

4.9, 3.58, 2.61, 1.89, 1.38, 1, 0.73 Sleeper Cab - Mid Roof Sleeper Cab - Lo w Roof Day Cab - High Roof Day Cab - Mid Roof Day Cab - Lo w Roof Class 7 Day

Cab - High Roof 2017 MY 13L***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 74 Com bination Day

Cab - Mid Roof Engine with 350 HP Day Cab - Lo w Roof HHD Vocational Regional Duty Cycle 2017 MY 15L Engine with 455 HP Multi - Purpose Duty Cycle 2017 MY 11L Engine with 345 HP 5 speed HHD

Automatic Transmission 4.6957 , 2.213 ,

1.5291 , 1 , 0.7643 Urban Duty Cycle MHD Vocational Regional Duty Cycle 2017 MY 7L Engine with 270 HP 5 speed MLHD

Automatic Transmission 3.102 , 1.8107 ,

1.4063 , 1 , 0.7117 Multi - Purpose Duty Cycle Urban Duty Cycle LHD Vocational Regional Duty Cycle 2017 MY 7L Engine with 200 HP Multi - Purpose Duty Cycle Urban Duty Cycle In GEM the cycle work from the powertrain testing will be corrected for the electrical and mechanical accessory power according to the follow ing equation. The accessory power is defined for each vehicle category in C hapter 4 of th is RIA.

= − ∙ ∙ . ( ) ( ) GEM will use the calculated cycle work and N / V of the powertrain for the to - be certified vehicle to interpolate the powertrain input table . For vehicle configuration s that have cycle work or N / V outside of the powertrain input table , we are proposing that the closest end points of the table be used instead of extrapolating. GEM will then use the following equation to calculate the CO 2 g/ton - mile result per cycle before any technology

inputs are applied. Finally the technology inputs are applied , all the cycles are weighted and the gallons of fuel are then calculated from the mass of CO 2 .

= h ∙ ∙ 1

∙ ∙ 

### 3.7 **Hybrid Powertrain Test Procedures** As discussed in Section V of the preamble , the agencies see an opportunity to help drive the technology ’s advancement by predicating the vocational vehicle standards on a small adoption rate of h ybrid powertrains in this rulemaking. However, since the projected effectiveness of this technology over the proposed Urban vocational duty cycle is 25 percent, the agencies believe it is no longer appropriate to provide a 1.5 multiplier for credits generated b y vehicles appl yi ng this technology . EPA and NHTSA are proposing two methods to demonstrate benefits of a h yb rid powertrain

– chassis and engine testing.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 75 

### 3.7.1 **Measurement Method and Results** T he agencies are proposing that h ybrid powertrains be t ested just like conventional powertrains, with the dy

namometer connected at either the input shaft of the rear axle or the input shaft to the wheels , using the powertrain method described in Section 3.6 with some additional requirements for the rechargeable energy storage sy stems (RESS) net energy change (NEC) over the test. As in the Phase 1 rule, the agencies are proposing that hy brids wil l be tested under charge sustain operation so that all the energy to drive the cycle comes from the on board hy brid powertrain. T he NE C of the RESS must meet the requirements of SAE J2711 for each test . 

### 3.7.2 **Engine Hybrid Method**  To address h ybrid powertrain sy stem performance for hy brids that recover energy between the engine and transmission , the agencies are proposing to retain the engine h ybrid procedures defined in 40 CFR 10 36 .525 . The control volume for these h ybrids is drawn so as to include the battery , battery support and control s ys tems, power electronics, the engine, motor generator and h ybrid control module. The performance of this s ys tem is an engine based evaluation in which emission rates are determined on a brake - specific work basis. As such, the duty cycles being proposed to assess this sy stem performance are engine speed and torque command cycles that are similar but not identical to the cycles used for criteria pollutant standards . In addition to the cycles being slightly different between the test for GHG emissions and the test for criteria emissions, the system boundary of the engine for the criteria emission test will remain unchanged and will not include the hy brid components. Itis expected that, parallel engine hy brids would be the mos t likely choice for engine - based hy brid certification. Details related to engine hy

brid test procedures may

be found in 40 CFR 1036.525.

**Figure 3**  **- 11**  **Engine Hybrid Test Configuration** ***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 76 

### 3.7.3 **Removal of the Chassis T**  **est O**  **ption for H** **ybrids** In the Phase 1 rule the agencies finalized a powertrain and chassis test option for hy brid testing . T he agencies are proposing to remove the chassis test option for the Phase 2 program because it appears to be incompatible with the proposed changes regarding use of results from the hy brid test procedure . In the proposed procedure , the output of the h ybrid test is brake specific CO 2 emission where the positive work is measured at the output shaft of the h ybrid powertrain. Since work cannot be measured at this location on a chassis dynamometer without modifying the vehicle, the agencies are proposing the removal of the chassis testing option. Another reason for the removal of the chassis test option is that there are a numb er of additional sources of variability

when testing a vehicle on a chassis dy namometer. These include e lectrical and mechanical accessory load, tire temperature and driver variability to name a few. 

### 3.7.4 **Electrified PTO Test Method** A power take off (PTO) is a sy stem on a vehicle that allows energy to be drawn from the vehicle’s drive s ys tem and used to power an attachment or a separate machine. Ty picall y in a heav y- duty truck, a shaft runs from the transmission of the truck and operates a hydraulic pump. The operator of the truck can select to engage the PTO shaft in order for it to do work, or disengage the PTO shaft when the PTO is not required to do work. The pressure and flow from this hydraulic fluid can be used to do work in implements attached to the truck. Common examples of this are utility trucks that have a lift boom on them, refuse trucks that pick up and compact trash, and cement trucks that have a rotating barrel. In each case the auxiliary implement is ty

pically pow ered b y a PTO that uses energy from the truck’s primary drive engine. In most PTO equipped trucks, it is necessary to run the primary

drive engine at all times when the PTO might be needed. This is an unoptimized configuration . Ty pical PTO sy stems requi re no more than 19 kW at any time, which is far below the optimal operation range of the primary drive engine of most trucks. Furthermore, in intermittent operations, the primary drive engine is kept running at all times in order to ensure that the PTO can operate instantaneousl y. This results in excess GHG emissions and fuel consumption due to idle time. Additionally , idling a truck engine for prolonged periods of time while operating auxiliary equipment like a PTO could cause the engine to cycle into a higher idle speed, wasting even more fuel. H yb ridiz ation and chang ing the operation of a conventional PTO equipped truck are two viable means to lower the GHG emissions and fuel consumption in the real world . The proposed test procedures will allow for manufactures to quantify the reduction of CO 2 emissions and fuel consumption from electrified PTO sy stems . In Phase 1, h ybrid PTO testing was performed either via chassis or powertrain testing of both the conventional and hy brid s ys tem s over the PTO duty cycles described in Appendix II of 40 CFR 1037 , in addition to the vehicle duty cycles . An improvement factor was then generated as described in 40 CFR 1037.615 and applied to the g/ton - mile CO 2 emission rate resulting from the GEM output for the advanced vehicle as described in 40 CFR 1037.520 . EPA and NHTSA are proposing to continue the Phase 1 testing methodology outlined in 40 CFR 1037.525 where A to B testing is used to generate an improvement factor either via***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 77 powertrain or chassis testing. The one change that the agencies are proposing for Phase 2 is how the results are used to calculate the vehicle ’ s emission result. For Phase 2, the agencies are proposing that the reduction in emission s from the electrified PTO s ys tem versus the convent ional PTO sy stem be subtracted from the composite driving emissions result. Specifics on the applicab ility of electrified PTOs is discussed further in Chapter V . C of the preamble . 

### 3.8 **Rear Axle Efficiency Test** In Phase 2, the agencies developed test procedur es to measure axle efficiency . See 40 CFR 1037.515 . This procedure ultimatel y provides for the determination of torque loss versus input speed and input torque for use in the GEM simulation tool. The procedure pro vides limitations on axle break in proce dures and prescribes dy namometer set ups for axles with and without lockable differentials as well as drive - through axles. This procedure puts limitations on the test cell ambient temperature, sump oil temperature, and requires the use of representative c ommerciall y available axle lubricating oil. The mapping process requires that you map the axle by testing with an input torque in the range of 0 to 4000 Nm in 1000 Nm steps at wheel speeds that range from 50 rpm to the maximum wheel speed in 50 rpm steps. The procedure sweeps though the torque points at a given wheel speed from the minimum to the maximum torque point and back, with the process repeated twice for a given wheel speed. The four values generated at each speed and torque point are then averag ed resulting in one map point per wheel and output torque value. 

### 3.9 **HD Pick up Truck** 

**and Van Chassis Test Procedure** The agencies are proposing that HD pickup trucks and vans continue to demonstrate compliance using the 40 CFR part 1066 chassis test procedures. For each test vehicle from a family required to comply

with the GHG and fuel consumption requirements, the manufacturer would supply

representative road load forces for the vehicle at speeds between 15 km/hr (9.3 mph) and 115 km/hr (71.5 mph). The road load force would represent vehicle operation on a smooth level road, during calm winds, with no precipitation, at an ambient temperature of 20 °C (68 °F), and atmospheric pressure of 98.21 kPa. Road load force for speed s below 9.3 mph may be extrapolated. The dy namometer's power absorption would be set for each vehicle's emission test sequence such that the force imposed during dynamometer operation matches actual road load force at all speeds. Required test dy namometer inertia weight class selections are determined by the test vehicle test weight basis using adjusted loaded vehicle weight from which the corresponding equivalent test weight is determined . 

### 3.9.1 **LHD FTP and HWFE Testing** The FTP dynamometer schedule consists of two tests, a “cold” start UDDS test a fter a minimum 12 - hour and a maximum 36 - hour soak according to the provisions of 40 CFR 1066.801, 1066.815, and 1066.816, and a “hot” start test following the “cold” start after a 10 minute soak. Engine startup (with all accessories turned off), operation over the UDDS, and engine shutdown constitutes a complete cold start test. Engine startup and operation over the first 505 seconds of the driving schedule complete the hot start test. The driving schedule for***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 78 EPA’s Urban Dy

namometer Driving Schedule is contained in Appendix Iof 40 CFR part 86. The driving schedule is defined b y a smooth trace drawn through the specified speed versus time relationship. The schedule consists of a distinct non - repetitive series of idle, acceleration, cruise, and deceleration modes of various time sequences and rates. The Highway

Fuel Economy

Dy namometer Procedure (HFET) consists of preconditioning highway driving sequence and a measured highway driving sequence. The HFET is designated to simulate non - metropolitan driving with an average speed of 48.6 mph and a maximum speed of 60 mph. The cycle is 10.2 miles long with 0.2 stops per mile and consists of warmed - up vehicle operation on a chassis dy namometer through a specified driving cycle. The Highway

Fuel Economy

Drivin g Schedule is set forth in Appendix Iof 40 CFR Part 600, while the test is carried out according to 40 CFR 1066.840. The driving schedule is defined b y a smooth trace drawn through the specified speed versus time relationships. Practice runs over the pre scribed driving schedules may be performed, provided an emission sample is not taken, for the purpose of finding the appropriate throttle action to maintain the proper speed - time relationship, or to permit sampling s ys tem adjustment. Both smoothing of spe ed variations and excessive accelerator pedal perturbations are to be avoided. The driver should attempt to follow the target schedule as closel y as possible. The speed tolerance at an y gi ven time on the dy namometer driving schedules specified in Appendi x I of parts 86 and 600 is defined by upper and lower limits in 40 CFR 1066.425. The upper limit is 2 mph higher than the highest point on trace within 1 second of the given time. The lower limit is 2 mph lower than the lowest point on the trace within 1 second of the given time. Speed variations greater than the tolerances (such as may occur during gear changes) are acceptable provided they

occur for less than 2 seconds on any occasion. Speeds lower than those prescribed are acceptable provided the veh icle is operated at maximum available power during such occurrences. 

### 3.9.2 **LHD FTP and HWFE Hybrid Testing** Since LHD chassis certified vehicles share test schedules and test equipment with much of L ight - Duty

Vehicle testing, EPA believes it is appropriate to co ntinue to use the HD Phase 1 test procedure which references SAE J1711 “Recommended Practice for Measuring the Exhaust Emissions and Fuel Economy of Hy brid - Electric Vehicles, Including Plug - in Hy brid Vehicles” instead of SAE J2711 “Recommended Practice for Measuring Fuel Economy and Emissions of Hy brid - Electric and Conventional Heavy- Duty Vehicles”. 

### 3.9.2.1 **Charge Depleting Operation –**  **FTP or “City” Test and HFET or “Highw**  **ay” Test** EPA would like comment on incorporating b y reference SAE J1711 C hapters 3 and 4, as p ublished June 2010, testing procedures for Light - Heav y- Duty chassis certified vehicles with the following exceptions and clarifications: Test cycles will continue, until the end of the phase of the test cycle , in which charge sustain operation is confirmed . Charge sustain operation is confirmed when one or more phases***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 79 or cycles satisfy

the Net Energy

Change requirements below. Optionally , a manufacturer may terminate charge deplete testing before charge sustain operation is confirmed provided that the Rec hargeable Energy

Storage S ys tem (RESS) has a higher State of Charge (SOC) at charge deplete testing termination than in charge sustain operation. In the case of Plug - In Hy brid Electric Vehicles (PHEV) with an all - electric range, engine start time will be recorded but the test does not necessarily

terminate with engine start. PHEVs with all electric operation follow the same test termination criteria as blended mode PHEVs. Testing can only be terminated at the end of a test cycle. The regulation allows E PA to approve alternate end of test criteria as described in 40 CFR 1066.501 . For the purposes of charge depleting CO 2 and fuel efficiency testing, manufacturers may elect to report one measurement per phase (one bag per UDDS). Exhaust emissions need not be reported or measured in the phases of the test the engine does not operate. End of test recharging procedure is intended to return the RESS to a full charge equivalent to pretest conditions. The recharge AC watt hours must be recorded throughout the charge time and soak time. Vehicle soak conditions must not be violated. The AC watt hours must include the charger efficiency . The measured AC watt hours are intended to reflect all applicable electricity consumption including charger losses, battery and vehicle conditioning during the recharge and soak, and the electricity consump tion during the duty cycles. Net Energy

Change Tolerance (NEC), is to be applied to the RESS to confirm charge sustaining operation. The agencies are proposing to continue to use the 1 percent of fuel energy NEC state of charge criteria as expressed in SAE J1711 and described in 40 CFR 1066.501. The Administrator may

approve alternate NEC tolerances and state of charge correction factors. 

### 3.9.2.2 **Hybrid Charge Sustaining Operation –**  **FTP or “City” Tes t and HFET**  **or “Highw ay” Test**  The agencies are proposing to continue incorporating b y reference SAE J1711 C hapters 3 and 4 for definitions and test procedures, respectively , where appropriate, with the following exceptions and clarifications. The agencies are adopting the 1 percent of fuel energy NEC state of charge criteria as expressed in SAE J1711 and described in 40 CFR 1066.501. The Administrator may approve alternate NEC tolerances and state of charge correction factors. Preconditioning special proc edures are optional for traditional “warm” test cycles that are now required to test starting at full RESS charge due to charge depleting range testing. If the vehicle is equipped with a charge sustain switch, the preconditioning cycle may be conducted pe r 40 CFR 600.111 provided that the RESS is not charged. Exhaust emissions are not taken in preconditioning drives. Alternate vehicle warm up strategies may be approved by

the Administrator. State of Charge tolerance correction factors may be approved b y the Administrator as described in 40 CFR 1066.501. RESS state of charge tolerances beyond the 1 percent of fuel energy may be approved by

the Administrator.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 80 The agencies are seeking comment on modifying the minimum and maximum allowable test vehicle accumulated mileage for both EVs and PHEVs. Due to the nature of PHEV and EV operation, testing may

require man y more vehicle miles than conventional vehicles. Furthermore, EVs and PHEVs either do not have engines or may use the engine for onl y a fraction of the miles driven. Electric Vehicles and PHEVs are to be recharged using the supplied manufacturer method provided that the methods are available to consumers. This method could include the electricity service requirements such as service amperage, voltage , and phase. Manufacturers may employ the use of voltage regulators in order to reduce test to test variability with prior Administrator approval. 

### 3.10 **Alternative Certification Approach 3.10.1**  **Purpose and Scope** Under the Phase 1 rule, vocational vehicle s and tract ors are certified b y using GEM with the default engine fuel map pre - defined by the agency , while the engine is certified by either using the SET cycle for tractor engines or the FTP cycle for vocational engines, which are totally different from vehicle dri v e cycles. Inthis section, a new concept as an alternative to the engine fuel mapping test , proposed in Phase 2 is explored. This approach would allow use of the same driv e cycles for both the vehicle and engine compliance process, without the need f or engine manufacturer providing the steady state engine fuel map for vehicle certification. Therefore, this approach has the potential to totally integrate vehicle and engine certification, while more accuratel y quantifying the transient engine operation than is possible using a traditional steady state engine fuel map . The potential approach discussed here would be an alternative to certifying vocational vehicles , tractors, and their engines using a steady- state fuel map . The agencies solicit c omment on this alternative, and commenters should include their thoughts on whether this concept can be adequatel y fleshed out in the time remaining in this rulemaking. 

### 3.10.1.1 **Phase 1**  **Certification Approach** In order to help to understand the vocational vehicle and tractor vehicle certification proc ess under the Phase 1 rule , Figure 3 - 12 summarizes the GEM - based certification process flow .***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 81 **Figure 3**  **- 12**  **Phase 1 Rule for Certification Using GEM** ***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 82 In this approach, vehicle manufacturers can onl y use up to five input parameters

– aero dy namic coefficient, rolling resistance, weight reduction, speed limiter, and idle reductio n, to conduct vehicle certifications (although improvements not recognized b y GEM can be certified as off - cycle credits under the Phase 1 rules) . All other vehicle and engine parameters are the default parameters specified by the agencies. Figure 3 - 12 show s that use of the agencies’ default engine fuel maps under the Phase 1 rules . This default engine fuel map approach would not be able to recognize the benefits of advanced engine technologies packages. The three drive cycles shown in Figure 3 - 12 used in Phase 1 are 55 mph and 65 mph cruise speed cycles, and ARB transient cycles. In the two cruise speed cycles, there is no road grade, meaning that the vehicle operates with one single operating point inside engine fuel maps, which does not represent the real - life driving condition on the road. On the other hand, engine certificati ons use completely different cycles. For example, tractor engine s use the SET cycle, while vocational engine s use the FTP cycle. Those engine cycles have very

little connection with how the engine operates in a vehicle over Phase 1 vehicle driv e cycles. This means whatever the optimized engine calibration developed for the FTP and SET cycles cell may

not be able to be realized in the real - life driving condition on the road. Furthermore, there is no direct linkage between GHG emissions and criteria emissions, since vehicle and engine certification cycles are different. 

### 3.10.1.2 **Primary Certification Approach in Phase 2**  In order to overcome the deficiencies mentioned in the above section, the agencies are proposing significant improvements and enhancements as part of the Phase 2 proposal . Man y of the Phase 1 predefined parameters used in GEM now become the vehicle - specific user - entered inputs in Phase 2. Most significantl y, vehicle manufacturers can use engine fuel maps representing the actual engine in the vehicle for certification, which means that it can recognize the benefits due to advanced techno logies developed for the engines. Chapter 4 of th is draft RIA details the enhancements of GEM and the extensive validations of these proposed changes . Another significant proposed enhancement is the addition of the road grade into 55 mph and 65 mph cruis e speed cycles, which represents more realistic driving condition s . In addition, the agencies propose reweighting on the SET cycles with more emphasis on A and B speed modes. The more detailed description on addition of the SET and road grade weighting c an be seen in Section II.D(1) and Section III.C of the preamble , respectivel y. Even with these improvements, however, certain issues would not be directly addressed. First of all, there would still be no direct linkage between GHG emissions and criteria pollutant emissions, since vehicle and engine certification cycles would still be different . Second, the engine fuel maps used in GEM from individual vehicle manufacturers are still obtained under steady state conditions. The transient behaviors due to s moke control and thermal management control, for example, would not be able to be modeled using steady state engine fuel maps. Third, the agencies’ primary certification approach introduces a new concern from independent engine manufacturers, namely conce rn regarding proprietary technology

information that can be found from engine fuel maps.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 83 

### 3.10.2 **Description of Alternative Certification**  **Concept** In view of these concerns mentioned above two sections for both Phase 1 and Phase 2, the agencies would like to specif icall y ask for comments on this alternative approach to Phase 2 certification to address these concerns. This section will introduce the concept and principal of this alternative approach.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 84 

### 3.10.2.1 **Vehicle Certification** 

**Figure 3**  **- 13**  **Alternative Phase 2**  **Certification Option II** 

**Figure 3**  **- 14**  **Phase 2 Certification Process with Option II******* E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 85 Displayed in Figure 3 - 13 and Figure 3 - 14 is the potential alternative vehicle certification approach. The entire process can be further simplified and described as follows.

1. Define nine vehicles that will cover the range of vehicles that the engine will be certified in. In one dimension the vehicles will cover the range of engine cycle work (W) b y varyi ng the vehicles mass, C d A and C

rr . The other dimension would cover the range of average engine speed over average vehicle speed (N/V), by varying the vehicles tire size and rear axle ratio or transmission (see the left part of Figure 3 - 13 ). 2. Run GEM with the nine vehicle configurations and the three certification cycles to generate 27 engine cycles (three certification cycles multiplied by nine vehicles). Each cycle will define engine speed and torque as a function of time. These cycles will be generated at 10hz to capture engine torque during shifting (see the right part of Figure 3 - 13 ). 3. Test the parent engine of the engine famil y using the 27 engines cycles to create a matrix of brake specific CO 2 consumption in g/hp - hr as a function of Work in hp hr and N/V in rpm/(mile/hr). 4. For certification, run GEM for each vehicle that will be certified with an engine from the e ngine family . For each simulation the actual vehicle parameters shall be used. The output of the simulation will be work in hp - hr and N/V in rpm/(mile/hr) for each drive cycle (See the left part of Figure 3 - 14 ). 5. Use work and N/V obtained from Step 4 to interpolate CO 2 in g/hp - hr for the engine in the specific vehicle being certified (see the middle part of Figure 3 - 14 . 6. Multiply

the interpolated CO 2 in g/hp - hr by work in (hp - hr) from the simulation of the certified vehicle (Step 4) and divide b y the ton - miles of each vehicle category and drive cycle (see the right part of Figure 3 - 14 ). 7. Supply

this final CO 2 in g/ton - mile for certification. 

### 3.10.2.2 **Engine C**  **ertification** One of the key

features for the alternative vehicle certification approach is that supplement ation of the engine tests requires running a number of tests at a certified engine dy no. These tests will result in a fuel consumption or CO 2 map in g/kw - hr as function of cycle work and N/V over three certification cycles. Therefore, the engine certification point could be selected from one of the testing points through this fuel consumption or CO 2 map, and therefore there is no need to run engine certification test alone, thus reducing engine t est burden from manufacturers as far as GHG emission certification is concerned. How this single point is to be selected is something we need to work out in the near future. 

### 3.10.3 **Discussion of Alternative Certification Approach** The previous section only describes the princip les of this alternative approach. This section will provide more detailed supporting information , addressing the following questions:***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 86  Would the fuel consumption or CO 2 maps be very well behave d , so that the interpolation or curve fitting can be carried out without losing accuracy?  Would one map that combines all three certification cycles be adequate to represent the engine or would an individual map for each cycle be needed?  What would be the most suitable independent axis of the fuel con sumption maps to be used to minimize the impact of type of transmissions and their shifting strategies?  What is the minimum number of engine tests and GEM simulations require d to cover the range of vehicles certifi ed for a given engine family? In order to answer the above questions, a test matrix based on a Class 8 Kenworth T700 tractor with a Cummins ISX engine was carefully designed as follows:

• 32 variations of the Kenworth T700

– Axel ratio: 2.64, 3.36,3.9 and 4.56

– C d : 0.35, 0.45, 0.55, 0.65, and 0.75

– C rr : 0.005, 0.006, 0.007 and 0.008 • Cycles

– with distance correction

– 55 w/SwRIgrade profile

– 65mph w/SwRIgrade profile

– ARB Transient • Transmissions

– Eaton AMT

– 10 speed: F016E310C - LAS

– 13 speed: FO_16E313A_MHP

– 18 speed: FO - 16E318B - MXP • Transmission shift strategy

– Eaton’s table shift

– EPA’s shift optimizer In addition, a child rating engine is selected to show its impacts on the accuracy of this approach. This results in a t otal of 1,152 simulation runs. 

### 3.10.4 **GEM Simulations** Phase 2 GEM (as proposed) was used by EPA to perform a large scale of simulations based on the matrix proposed above. The results and plots are arranged as follows. Figure 3 - 15 to Figure 3 - 17 display

the BSFC (g/hp - hr) surface plots over 55mph, 65mph, and ARB cycles with all points simulated. The next section discusses the evaluation of the results with the engine child ratings.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 87 **Figure 3**  **- 15**  **Contour plot of CO 2**  **as function of cycle work and N/V for 55 m ph cycle** 

**Figure 3**  **- 16**  **Contour plot of CO 2**  **as function of cycle work and N/V for 65 m ph cycle** 

20 25 30 20 25 30 35 40 45 140 150 160 170 180 190 200

Wo rk ( hp-hr) 55m ph

N/V ( rpm /( km/h r))bsfc(g/hp-hr) bs fc

450hp rat in g

15 20 25 30 25 30 35 40 45 50 140 150 160 170 180 190 200

Wo rk ( hp-hr) 65m ph

N/V ( rpm /( km /h r))bsfc(g/hp-hr) bs fc

450hp rat ing***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 88 **Figure 3**  **- 17**  **Contour plot of CO 2**  **as function of cycle work and N/V for ABB cycle** As can be seen from these three figures ( Figure 3 - 15 to Figure 3 - 17 ), a surface is used to curve fit all points. Also s hown in these figures is how well the actual points are fitted with the surface. It is seen from Figure 3 - 15 and Figure 3 - 17 that all test cycles are collapsed into one surfa ce with different transmissions, differe nt shifting strategies, and axles. The behavior that all simulation points are very well fitted into one surface plane suggests that impact of transmissions including shifting strategies and numbers of gears, axle ratio be minimal if the plots are designe d in such a way

that average engine speed ( N ) over average vehicle speed ( V ) defined as N

/ V is selected. Figure 3 - 18 shows the three - dimensional surface plot of BSF C as function of cycle work and N / V with all cycles combined into one plot. It can be seen that all points are not very well fitted into one surface plot, suggesting that certification be done in an individual cycle manner. 60 70 80 90 11. 5 12 12. 5 13 13. 5 14 14. 5 170 175 180 185 190 195 200 205 210

Wo rk ( hp-hr) AR B

N/ V ( rpm /( km/h r))bsfc(g/hp-hr) bs fc

450hp rat ing***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 89 **Figure 3**  **- 18**  **Surface plot of CO 2**  **as function of cycle work and N/V for all three cycles** The simulations are then carried out in order to address child rating impact on this surface fit with each cycle. Figure 3 - 19 to Figure 3 - 21 show the behavior of all three individual cycles. It can be seen that all pare nt and child rating points are still collapsed into one surface plot, which is very

similar to the results where onl y parent ratings are shown in Figure 3 - 16 to Figure 3 - 18 , suggesting that the same interpolation schemes or the same surface fitting could be applied to both parent and child ratings for those points that are loc ate d between the testing points. 20 40 60 80 10 20 30 40 50 140 160 180 200 220 240 260 280

Wo rk ( hp-hr) All C ycl es

N/V ( rpm /( km/h r))bsfc(g/hp-hr) bs fc 450hp rat ing***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 90 **Figure 3**  **- 19**  **Surface plot of CO 2**  **with child rating engine for 55m ph cycle** 

**Figure 3**  **- 20**  **Surface plot of CO 2**  **with child rating engine N/V for 65 m** **ph cycle**

20 25 30 20 25 30 35 40 45 145 150 155 160 165 170 175 180 185 190 195

Wo rk ( hp-hr) 55mph

N/ V ( rpm /( km/h r))bsfc(g/hp-hr) bs fc

400hp rat in g 450hp rat in g

15 20 25 30 25 30 35 40 45 50 140 150 160 170 180 190 200

Wo rk ( hp-hr) 65m ph

N/ V ( rpm /( km/h r))bsfc(g/hp-hr) bs fc

400hp rat in g 450hp rat in g***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 91 **Figure 3**  **- 21**  **Surface plot of CO 2**  **with child rating engine for ABB cycle** Figure 3 - 19 to Figure 3 - 21 demonstrate the well behaving nature of CO 2 surface as a function of work and N/V as lo ng as the surface fitting is conducted in an individual cycle, showing the potential to use surface fitting or interpolation scheme to determine the point resulted from the actual vehicle certification. However, please note that the entire simulations con sist of over one thousand points, and it would be impossible to run all engine tests in order to generate a CO 2 map for use in certification . Efforts must be made to greatly simplify the process by reducing the points to a minimum level, which can still v ery well represent a to - be - certified vehicle. After numerous trials, it is found that a minimum 9 points per cycle is needed, which covers three final drive ratios and three vehicle loads or work. Displayed in Figure 3 - 22 to Figure 3 - 24 are the same plots as Figure 3 - 19 to Figure 3 - 21 , but the numbers of points are reduced to 9 points per cycle. 60 70 80 90 11. 5 12 12. 5 13 13. 5 14 14. 5 170 175 180 185 190 195 200 205 210

Wo rk ( hp-hr) AR B

N/ V ( rpm/ (k m/hr))bsfc(g/hp-hr) bs fc

400hp rat ing 450hp rat ing***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 92 **Figure 3**  **- 22**  **Contour plot of CO 2**  **with only 9 points for 55m ph cycle** 

**Figu re**  **3 -**  **23 Contour plot of CO**  **2 with only 9 points N/V for 65 m** **ph cycle** 20 25 30 20 25 30 35 40 45 140 150 160 170 180 190 200

Wo rk ( hp-hr) 55mph

N/ V ( rpm /( km /h r))bsfc(g/hp-hr) bs fc All Po in ts 9 Points

15 20 25 30 25 30 35 40 45 50 140 150 160 170 180 190 200

Wo rk ( hp-hr) 65mph

N/ V ( rpm /( km /h r))bsfc(g/hp-hr) bs fc

All Po int s 9 Po ints***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 93 **Figure 3**  **- 24**  **Contour plot of CO 2**  **with only 9 points for ABB cycle** Comparing Figure 3 - 19 to Figure 3 - 21 , very similar behaviors for all three cycles are observed, and therefore, it can be sai d that 9 points would be acceptable at least for the engine s and vehicles that are under consideration. 

### 3.10.5 **Generic Vehicle Definition**  Chapter 3.10.4 shows that nine vehicle configurations for each certification cycle could be used to cover the range of the vehicles to be certified. However, it is not clear how those vehicle configurations can be defined in a generic way . This section attempts to achieve this object ive. To cover the range of vehicle configuration that the engine could be sold in the agencies are considering the vehicle configuration defined in Table 3 - 30 to Table 3 - 32 . To cover the range of axles, the axle ratios would be calculated from the regulatory defined engines speeds and the maximum duty

cycle speed of 65 mph. Wi th the engine speed, tire radius, top gear ratio and vehicle speed, the axle ratio can be calculated. To cover the range of engine work the agencies are proposing a range of drag area ( C d A ), coefficients of rolling resistance ( C rr) and vehicle masses. Fo r Class 8 vehicles the highest mass and highest C d A be on the same vehicle and that both C

d A and vehicle mass drop together for the lower average power vehicles. The reason for this is that, the cruise cycle’s average power is most affected by the vehicle’s C

d A , where mass has the largest effect on average power on the transient cycle. For Clas s 2b - 7 60 70 80 90 11. 5 12 12. 5 13 13. 5 14 14. 5 170 175 180 185 190 195 200 205 210

Wo rk ( hp-hr) AR B

N/ V ( rpm /( km/h r))bsfc(g/hp-hr) bs fc

All Po in ts 9 Po int s***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 94 vehicles mass and C rr are varied to change the average power over the cycle. For these vehicles C rr is varied instead of C d A because C

d A is not an input into GEM for vocational vehicles. In addition to defining the vehicle parameters the agencies a re proposing that the transmissions be defined for each vehicle configuration. T able 3 - 34 defines the transmission ty pe and gear ratios for each of these vehicles. **T able**  **3 -**  **34 Default Transm** **issions** GEAR NUMBER TRANSMI SSI ON TYPE AND GEAR RATIO S

10 speed AMT 6 speed HH AT 6 speed MH AT 1 12.8 4.6957 3.102 2 9.25 2.213 1.8107 3 6.76 1.5291 1.4063 4 4.9 1 1 5 3.58 0.7643 0.7117 6 2.61 0.6716 0.61 7 1.89 N/A 8 1.38 9 1 10 0.73 

### 3.10.6 **Certification Point Determination from Alternative** Table 3 - 30 to Table 3 - 32 define the numbers of vehicle configurations so that a well defined map can be generate d for a certain vehicle family to be certified. Section 3.10.4 shows that a surface fitting could approximate the surface for the entire vehicle applications. It indicates that the fitted surface could be well behaved onl y if an individual cycle is plotted. However, it can be imagined that the surface could be distorted if those mapping points shown in Table 3 - 30 to Table 3 - 32 may not be general enough to define the range of applications. As a result, an alternative to surface fitting should be considered. This section discusses a numerical scheme that is used to determine to - be - certified CO 2 of the vehicle famil y from the CO 2 map generated from the engine tests as well as GEM simulation. It should be pointed o ut that the numerical scheme discussed in this section is only the first attempt to derive a numerical scheme that can interpolate or extrapolate certification point, and many other alternatives and optimization schemes can be used as well. In the approach , it is assumed that one map per certification cycle is considered, each consisting of 8 - 9 data points, but the map data does not need to be in an exact rectangular matrix or in any particular order. In order to demonstrate the concept, the generic vehicl e defined in Table 3 - 31 is used, where there are a total of nine configurations as shown in Figure 3 - 25 to Figure 3 - 27 for three certification cycles . Shown in these figures are also a number of vehicle***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 95 configurations that could be certified under this map, covering a wide range of applications including both tractor and vocational vehicles and different transmissio n packages. In these figures, X axis is SN/SV defined as average engine speed over average vehicle speed in r pm/km - ph . Y axis is the cycle work in kw - hr over the individual driving cycle. T he legend of “ Map Points ” stands for the generic class 8 nine vehicle configurations using the same engine defined in Table 3 - 31 . In these transmission packages, the same engine as the generic vehicle is used, and vehicle variables are varied, such as tire, axle, and aerody namic packages. Veh 1 and Veh 2 stand for class 8 vehicles for ty pical vocational applications using the same engine as the generic vehicle . They all have similar vehicle weight, but with different tires, axle ratio s , and aerodynamic packages. The purpose of these practices is to demonstrate whether the generic vehicl e points (Map Points) can be used to interpolate or extrapolate all other points under different vehicle and transmission configuration s with a high confidence level . From these figures, it can be seen that quite a few vehicle configurations are outside g eneric vehicle points, which are shown in “Map Points”. This means that extrapolations must be used. It is hoped that whatever numerical scheme is used can offer reasonably good accuracy in terms of interpolation as well as extrapolation.

**Figure 3**  **- 25**  **Alternative certification m ap for 55 m** **ph certification cycle** 16.0 17.0 18.0 19.0 20.0 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0

10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0kW-hr

SN/SV gC O2 /k W - hr Map Points Tr an 1 Veh 1 Veh 2 Tr an 2 Tr an 3***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 96 **Figure 3**  **- 26**  **Alternative certification m ap for 65 m** **ph certification cycl e** 

**Figure 3**  **- 27**  **Alternative certification m ap for ARB certification cycle**  19.0 20.0 21.0 22.0 23.0 24.0 25.0 26.0 27.0 28.0 29.0 30.0 31.0 32.0 33.0 34.0

10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0**k W** **- h** **r**

**SN /SV**  **gC O2/k**  **W -**  **hr** Map Points Tr an 1 Veh 1 Veh 2 Tr an 2 Tr an 3

5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0

37.5 38.5 39.5 40.5 41.5 42.5**k W** **- h** **r**

**SN/SV gC**  **O2/kW -**  **hr** Map Points Tr an 1 Veh 1 Veh 2 Tr an 2 Tr an 3***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 97 In order to prove the concept and numerical accuracy in determining appropriate CO 2 for certification, those nine points defined by Table 3 - 31 as shown in “Map Points” of these three figures which are used to interpolate or extrapolate CO 2 for an y other vehicle configurations points and then are compared wi th the actual simulation points. In the numerical scheme used in this study , within, above, and to the right of a mapped region defined by nine Map Points , interpolation and extrapolation occur in a plane defined by the interpolated point’s 3 - nearest mapp ed neighbors. Below and to the left of the mapped region extrapolation occur between the 2 nearest neighbors along the non - extrapolated axis and there is no change in the extrapolated value along an y extrapolated axis. The interpolation scheme is to pic k the 3 closest neighbors that have a maximum included angle less than 120 degrees , which eliminates picking the narrow triangular planes formed just outside of the mapped region. Table 3 - 35 , Table 3 - 36 , an d Table 3 - 37 show th e comparisons for those points. In these tables, there are 76 vehicle configurations. Among them, nine points with green color filled are the generic vehicle defined in Table 3 - 31 . All other points represent different vehicle configurations under the same engine family . The column with error (%) is the comparison of CO 2 g/hp - hr between the tes t points and interpolated or extrapolated values. For the sake of simplicity , both values of CO 2 g/hp - hr for both test and interpolated/extrapolate points are not shown in these tables. As can be seen from Table 3 - 35 and Table 3 - 36 , onl y one point shows over 4 percent numerical accuracy , and most points are under 2.5 percent diff erence for cruise speed 55 mph and 65 mph cycles, even for those points located outside mapped region. On the other hand, ARB cycle shows quite a few points in the range of 4 .0 - 4.5 percent difference , which is a concern as far as the certification is concerned . These results suggest that m ore work and numerical scheme development will be required moving forward.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 98 **Table 3**  **- 35**  **Proof of Concept and Numerical Sche**  **me Accuracy for 55MPH**  **Cycle INTERP/EXTRAP POI**  **NTS INTERP/EXTRAP POINTS**  **i**  **N/**  **V i**  **kW -**  **hr i**  **Error (%)**  **i**  **N/**  **V i**  **kW -**  **hr i**  **Error (%)**  1 12.61 27.37 0.5% 39 12.71 24.11 1.0% 2 12.31 27.73 - 0.4% 40 14.18 24.17 0.4% 3 13.30 27.78 - 0.2% 41 18.06 24.36 2.3% 4 12.47 23.81 1.6% 42 13.31 24.13 0.8% 5 12.31 24.09 1.0% 43 12.71 20.74 1.2% 6 13.30 24.13 0.8% 44 14.18 20.80 0.9% 7 12.42 20.46 1.8% 45 18.06 20.98 3.0% 8 12.31 20.72 1.7% 46 13.31 20.76 1.2% 9 13.30 20.76 1.2% 47 11.0727 20.474 0.5% 10 11.85 25.84 0.2% 48 11.3574 20.298 1.5% 11 12.80 25.89 0.3% 49 11.9048 20.342 1.9% 12 11.85 22.36 1.3% 50 12.8518 20.428 1.7% 13 12.80 22.40 1.6% 51 11.1814 22.769 0.3% 14 12.14 20.97 0.2% 52 11.3602 22.55 1.0% 15 12.04 21.19 - 0.3% 53 11.9048 22.609 1.5% 16 13.01 21.24 - 0.6% 54 12.8518 22.7 1.6% 17 14.19 21.30 - 2.1% 55 12.882 26.145 0.5% 18 19.26 21.61 - 2.0% 56 15.1703 21.851 - 0.7% 19 11.99 20.14 0.3% 57 17.4585 22.132 - 0.8% 20 12.04 20.33 - 0.2% 58 19.7468 22.449 - 1.8% 21 13.01 20.38 - 0.9% 59 22.0351 22.745 - 3.3% 22 14.19 20.44 - 1.6% 60 23.1592 22.9 - 4.0% 23 19.26 20.73 - 1.4% 61 18.3492 22.253 - 1.1% 24 11.98 19.36 0.4% 62 20.7542 22.579 - 2.8% 25 12.04 19.54 0.0% 63 15.9442 21.943 - 0.2% 26 13.01 19.59 - 0.3% 64 13.5392 26.215 0.4% 27 14.19 19.65 - 1.2% 65 10.8136 25.072 0.0% 28 19.26 19.93 - 0.9% 66 10.4952 19.698 0.0% 29 14.44 21.32 - 2.3% 67 10.4952 16.748 0.0% 30 14.90 21.34 - 2.9% 68 14.4455 26.005 0.0% 31 12.97 21.24 - 0.6% 69 14.4455 19.938 0.0% 32 17.08 21.47 - 1.4% 70 14.4455 16.927 0.0% 33 13.82 21.28 - 1.8% 71 19.5963 26.267 0.0% 34 18.55 21.56 - 1.7% 72 19.5963 20.22 0.0% 35 12.71 27.75 - 0.2% 73 19.5963 17.21 0.0% 36 14.18 27.82 - 0.5% 74 17.0015 26.129 1.5% 37 18.06 28.03 - 1.3% 75 17.0015 20.072 1.8%***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 99 38 13.31 27.78 - 0.2% 76 17.0015 17.061 2.0% **Table 3**  **- 36**  **Proof of Concept and Numerical Sche**  **me Accuracy for 65MPH**  **Cycle INTERP/EXTRAP POINTS**  **INTERP/EXTRAP POINTS i**   **N/**  **V i**  **kW**  

** hr** **i Error**  **(%) i**   **N/**  **V i**  **kW -**  **hr i**  **Error (%)**  1 11.40 32.68 0.6% 39 12.71 27.96 1.8% 2 12.31 32.85 - 0.9% 40 14.18 28.04 0.8% 3 13.30 32.94 - 1.2% 41 18.06 28.26 2.1% 4 11.40 27.86 0.9% 42 13.31 27.99 1.5% 5 12.31 27.93 1.8% 43 12.71 23.39 2.2% 6 13.30 27.99 1.5% 44 14.18 23.47 1.9% 7 11.40 23.33 1.5% 45 18.06 23.67 4.2% 8 12.31 23.38 2.1% 46 13.31 23.42 2.1% 9 13.30 23.42 2.1% 47 10.287 23.201 0.1% 10 11.85 30.33 1.1% 48 11.1382 23.307 1.3% 11 12.80 30.41 0.6% 49 11.9048 23.383 2.0% 12 11.85 25.57 1.9% 50 12.8518 23.471 2.3% 13 12.80 25.61 2.4% 51 10.4864 26.581 0.1% 14 11.15 27.02 1.1% 52 11.1382 26.689 0.9% 15 12.04 27.08 1.2% 53 11.9048 26.797 1.2% 16 13.01 27.13 1.7% 54 12.8518 26.895 2.3% 17 14.19 27.21 0.4% 55 12.882 31.126 0.1% 18 19.26 27.57 1.2% 56 15.1703 27.695 0.5% 19 11.15 25.75 1.2% 57 17.4585 28.007 1.6% 20 12.04 25.80 2.0% 58 19.7468 28.315 0.1% 21 13.01 25.86 0.7% 59 22.0351 25.395 2.3% 22 14.19 25.94 0.2% 60 23.1592 23.919 3.4% 23 19.26 26.30 1.0% 61 18.3492 28.124 2.0% 24 11.15 24.56 0.3% 62 20.7542 27.401 - 0.3% 25 12.04 24.61 1.5% 63 15.9442 27.802 1.0% 26 13.01 24.67 0.4% 64 13.5392 31.201 - 0.3% 27 14.19 24.75 - 0.3% 65 10.4952 29.49 0.0% 28 19.26 25.11 0.4% 66 10.4953 23.234 0.0% 29 14.44 27.23 0.0% 67 10.4952 19.715 0.0% 30 14.90 27.26 - 0.7% 68 14.4455 29.917 0.0% 31 12.97 27.13 1.8% 69 14.4456 23.441 0.0% 32 17.08 27.41 1.5% 70 14.4455 19.921 0.0% 33 13.82 27.18 0.8% 71 19.5963 30.142 0.0% 34 18.55 27.52 2.0% 72 19.5964 23.766 0.0% 35 12.71 32.89 - 1.0% 73 19.5963 20.247 0.0%***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 100 36 14.18 33.00 - 1.8% 74 17.0015 30.063 1.0% 37 18.06 33.20 - 1.6% 75 17.0016 23.594 0.6% 38 13.31 32.94 - 1.2% 76 17.0015 20.075 0.3% **Table 3**  **- 37**  **Proof Of Concept**  **a nd Numerical Sche**  **me Accuracy f**  **or ARB**  **Cycle INTERP/EXTRAP POINTS**  **INTERP/EXTRAP POINTS i**   **N/**  **V i**  **kW**  

** hr** **i Error**  **(%) i**   **N/**  **V i**  **kW -**  **hr i**  **Error (%)**  1 41.00 9.66 - 1.2% 39 39.26 9.29 - 2.7% 2 40.16 9.65 - 0.9% 40 40.34 9.30 - 1.3% 3 39.48 9.64 - 1.0% 41 40.56 9.33 - 1.9% 4 40.98 9.30 - 1.0% 42 39.49 9.28 - 2.5% 5 40.13 9.30 - 2.9% 43 39.23 8.92 - 2.3% 6 39.43 9.28 - 2.3% 44 40.31 8.93 - 2.6% 7 40.95 8.93 - 2.1% 45 40.53 8.97 - 2.8% 8 40.03 8.93 - 2.0% 46 39.00 8.91 - 2.0% 9 39.39 8.91 - 1.9% 47 39.1403 9.2227 1.0% 10 41.40 9.48 - 0.7% 48 40.0123 9.2143 0.4% 11 39.47 9.45 - 1.3% 49 39.2724 9.1879 0.7% 12 41.13 9.10 - 1.1% 50 38.9924 9.1411 1.0% 13 39.43 9.09 - 2.3% 51 39.2179 9.3688 0.4% 14 40.17 6.25 - 4.1% 52 40.0236 9.3563 0.2% 15 39.40 6.25 - 4.2% 53 39.3053 9.3359 0.4% 16 38.82 6.26 - 4.3% 54 38.9921 9.2828 0.9% 17 38.89 6.26 - 4.4% 55 39.1243 10.353 1.2% 18 40.73 6.32 - 3.9% 56 38.1574 7.0408 0.2% 19 40.03 6.17 - 4.5% 57 40.5059 7.0397 0.7% 20 39.40 6.17 - 4.5% 58 42.0372 7.087 1.2% 21 38.75 6.19 - 4.6% 59 43.4797 7.1226 1.6% 22 38.88 6.18 - 4.6% 60 43.1689 7.1632 0.9% 23 40.73 6.25 - 4.1% 61 44.334 7.1471 0.8% 24 40.02 6.11 - 4.8% 62 44.0081 7.1626 0.0% 25 39.31 6.11 - 4.7% 63 41.7231 7.0508 - 2.9% 26 38.75 6.12 - 4.8% 64 41.8206 10.136 1.5% 27 38.88 6.12 - 4.8% 65 39.4411 11.832 0.0% 28 40.73 6.18 - 4.4% 66 38.2432 8.6276 0.0% 29 39.85 6.27 - 4.2% 67 37.8895 7.3752 0.0% 30 40.32 6.29 - 3.9% 68 41.2466 11.14 0.0% 31 38.40 6.23 - 4.5% 69 40.3708 8.1927 0.0% 32 40.88 6.73 - 3.3% 70 40.0346 7.1138 0.0% 33 38.21 6.34 - 4.5% 71 42.1071 10.8 0.0%***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 101 34 41.58 6.69 - 2.9% 72 41.6921 8.0995 0.0% 35 39.31 9.65 - 1.3% 73 41.4929 7.0552 0.0% 36 40.36 9.66 - 1.3% 74 42.1548 10.83 0.2% 37 40.69 9.69 - 1.8% 75 41.6017 8.0873 0.4% 38 39.57 9.64 - 1.2% 76 41.4366 7.0472 0.4% 

### 3.10.7 **Preliminary Comparisons of Primary and Alternative Approaches**  The main purpose of introduction of this alternative approach for vehicle certification is to integrate vehicle certification with engine certification, being able to address both GHG emissions and criteria emission in one set of tests. Chapter 3.10.4 shows the princip le of this approach. However, one of the key questions remains

– how this alternative certification approach is credible in terms of accuracy as opposed to the primary vehicle certification approach? Inaddition, there are also many other questions that still need answer s , such as parent and child rating impacts, the impact of vocational sector with a large variation on the ratio of N/V (average engine speed over average vehicle speed), surface fit or interpolation scheme, and engine certification. Shown in Figure 3 - 28 is the comparison between alternative approaches discussed in this Section and GEM with steady state map based approach discussed in Chapter 4 of this draft RIA. In both engine and GEM simulations, a test matrix consisting of twenty seven points is tested (3 axle ratios x 3 C

d values x 3 cycles) as shown below.

• Nine variations of the Kenworth T700 to cover the range of vehicle loads

– Axel ratio: 2.64, 2.85, and 3.08

– C d : 0. 41, 0.55, and 0.7 • Three certification c ycles

– with distance correction

– 55 w/SwRIgrade profile

– 65mph w/SwRIgrade profile

– ARB Transient • Eaton AMT model: 10 speed: F016E310C - LAS***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 102 **Figure 3**  **- 28**  **Com parisons between Alternative and GEM Based Approaches**  **120 130**  **140 150**  **160 170**  **180 190** 

**130 140**  **150 160**  **170 180**  **190 E** **n g** **i n** **e B** **S F** **C (** **g /** **h p** **- h** **r )** **- G** **E M** 

**Engine BSFC**  **(g/ hp**  **- hr)**  **- measured**  **from Eng**  **ine tests 1:1**  **GE M**  **sim -**  **SS map**  **based Alternative**  **1:1 +5%**  **1:1 -**  **5%******* E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 103 As shown in Figure 3 - 28 , both alternative approach and GEM based approach seem to produce similar results in 55 mph and 65 mph cruise cycles with road grade. However, it is clearly shown that the alternative approach seems to be better in the transient cycle than GEM based approach with the steady state map. 

### 3.10.8 **Remaining Questions and Future Plans**  The comparison shown in Figure 3 - 28 onl y partially answers this alternative approach fidelity with one specific engine and transmission platform and because of this there are still many unanswered questions. The following questions are onl y a subset of the questions that need to be answered :  How does this alternative approach address parent and child rating? Would nine points be adequate to cover the practical range of the vehicle operation on the road?  How can this approach address those points that may be out of map ranges with much higher or lower N/V?  What kinds of numerical schemes, interpolation or surface fitting, shall be used to interpolate those points that are located between testing points?  What the numerical scheme shall be used to extrapolate those points outside the maps?  How robust are these numerical schemes?  Can what we have learned so far be applied to other engines?  How the single engine certification point shall be selected among the number of engine tests?  Are there potential unintended consequences? The agencies welcome comments on these questions and on the alternative vehicle certification approach in general.***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 104 

## References 1 For more information, see CFR Title 40, Part 86.004 - 28 2 National Renewable Energy Laboratory, 2014. Technical Report: Appending High - Resolution Elevation Data to GPS Speed Traces for Vehicle Energy Modeling and Simulation. http://www.nrel.gov/docs/fy14os ti/61109.pdf 3 Southwest Research Institute coastdow n and constant speed testing summary report for EPA. 4 R.M. Young. Product specifications for Ultrasonic Anemometer Model 81000. http://www.youngusa.com/products/6/3.html 5 SAE International, 2013, Guidel ines for Aerodynamic Assessment of Medium and Heavy Commercial Ground Vehicles Using Computational Fluid Dynamics, SAE J2966, 2013 - 09 6 2010 NAS Report. Finding 2 - 4 on page 39. 7 SAE International, 1987, Fuel Consumption In - Service Test Procedure Type III , SAE J1526, 1987 - 06 8 CARB -NREL Aero testing Report (2014) 9 U.S. EPA. Truck and Trailer Roof Height Match Analysis Memorandum from Amy Kopin to the Docket, August 9, 2010. Docket Identification Number EPA - HQ - OAR - 2010 - 0162 - 0045. 10 Ben Sharpe (ICCT) and Mike Roeth (North American Council for Freight Efficiency), “Costs and Adoption Rates of Fuel - Saving Technologies for Trailer in the North American On - Road Freight Sector”, Feb 2014. 11 Frost & Sullivan, “Strategic Analysis of North American Semi - trailer Advanced Technology Market”, Feb 2013. 12 EPA, 2011, HD Phase 1 Regulatory Impact Analysis, Figure 3 - 16. EPA - 420 - R - 11 - 901. 13 (http://webstore.ansi.org/RecordDetail.aspx?sku=ISO+28580%3a2009) 14 SAE International, 2006, Rolling Resistance measurement Procedure for Passenger Car, Light Truck, and Highway Truck and Bus Tires, SAE J1269, 2006 - 09 15 ISO, 2009, Passenger Car, Truck, and Bus Tyres

– Methods of Measuring Rolling Resistance

– Single Point Test and Correlation of Measurement Results : ISO 28580:2009(E), First Edition, 2009 - 07 - 01 16 NHTSA, 2009. “NHTSA Tire Fuel Efficiency Consumer Information Program Development: Phase 1

– Evaluation of Laboratory Test Protocols.” DOT HS 811 119. June. (www.regulations.gov, Docket ID: NHTSA 2008 - 0121 - 0019). 17 SAE International, 1999, Stepwise Coastdown Methodology for Measuring Tire Rolling Resistance, SAE J2452, 1999 - 06 18 ISO, 2005, Passenger Car, Truck, Bus, and Motorcycle Tyres

– Methods of Measuring Rolling Resistance, ISO 18164:2005(E) 19 SAE International, 2012, Test Procedures for Measuring Truck Tire Revolutions Per Kilometer/Mile, SAE J1025, 2012 - 08 20 Based on MOVES analysis. 21 Gautam, M., N. Clark, W. Riddle, R. Nine, S. Wayne, H. Maldonado, A. Agrawal, M. Carlock. “Development and Initial Use of a Heavy - Duty Diesel Truck Test Schedule for Emissions Characterization.” SAE Paper 2002 - 01 - 1753. 2002. 22 Governors Highway Safety Association. Speed Limit Laws May 2011. Last viewed on May 9, 2011 at http://www.ghsa.org/html/stateinfo/laws/speedlimit_laws.html 23 Environmental Defense Fund. “Greenhouse Gas Management for Medium - Duty Truck Fleets.” Viewed at http://edf.org/documents/10860_fleets - med - ghg - management.pdf. Page 6. 24 ICF International. Investigation of Costs for Strategies to Reduce Greenhouse Gas Emissions for Heavy - Duty On - Road Vehicles. July 2010. Pages 4 - 16. Docket Identification Number EPA - HQ - OAR - 2010 - 0162 - 0044. 25 M.J. Bradley & Associates. Setting the Stage for Regulation of Heavy - Duty Vehicle Fuel Economy and GHG Emissions: Issues and Opportunities. February 2009. Page 35. Analysis based on 1992 Truck Inventory and Use Survey data, where the survey data allowed developing the distribution of loads instead of merely the average loads. 26 The U.S. Federal Highway Adm inistration. Development of Truck Payload Equivalent Factor. Table 11. Last viewed on March 9, 2010 at http://ops.fhwa.dot.gov/freight/freight_analysis/faf/faf2_reports/reports9/s510_11_12_tables.htm***** E.O. 12866 Review –**  **REVISED –**  **Do Not Cite, Quote, or Release During Review *****

3 - 105 27 Excerpted from The U.S. Federal Highway Administration. Development of Truck Payload Equivalent Factor. Table 11. Last vie wed on March 9, 2010 at http://ops.fhwa.dot.gov/freight/freight_analysis/faf/faf2_reports/reports9/s510_11_12_tables.htm 28 The U.S. Federal Highway Administration. Development of Truck Payload Equivalent Factor. Table 11. Last viewed on March 9, 2010 at http://ops.fhwa.dot.gov/freight/freight_analysis/faf/faf2_reports/reports9/s510_11_12_tables.htm